What sort of bike do you ride, what condition is it in, how suited to the purpose is it and how familiar with its components are you?

Is your bike an odd thing imported from Moldavia and rife with obscure sizes and components, or is it an Acme Speed 2.0 with readily available bits and bobs? You can greatly assist your toolkit requirements by choosing your bike and components for the duty they will serve.

What is it reasonable to fix, what are you willing to fix and what are you willing to learn to fix are perhaps more important considerations that influence the toolkit you carry.

There is little point carrying a tool unless you know how to use it and you are willing to use it. On the one hand, it's probably unreasonable to expect repair a broken frame - though it has been done. On the other hand, it would be quite limiting were you unable to remove a wheel and fix a puncture.

I've seen riders willing to wait hours on a roadside for a sag wagon because they have run out of tubes, haven't the means, knowledge or will to patch a punctured tube - this is a basic skill. In addition to a good pump, it requires only a few grams of equipment, and the skills required are not rocket science.

As an urban commuter content to take your bike to the Local Bike Shop (LBS) to have its tyres inflated, to fix its punctures and to service your bike, then durable tyres and components in general will meet your carefree needs.

But, if you're doing an unsupported ride across the Nullabor, or through the rural backblocks far from your LBS, you might have greater need for a decent toolkit and the ability to use it.

Even so, there's a wide spectrum of on the spot repairs. I ride to the corner shops quite often with no tools, no pump, nothing at all. But I'd walk the bike the short distance home should I have any problems, even if I had tools. On the other hand I do regular rides of much greater distances and in rural areas (no mobile coverage) where it's help yourself or hitchhike home.

I've tried to come up with a toolkit and spares light enough and comprehensive enough to be a permanent fixture on my bike. I've made efforts to standardise bolts to reduce tool requirements, and to choose components for durability. For example, my wheels are 32 spoke using quality hubs and strong rims. Tyre sections are apt for my weight and performance needs. The tyre and rim combinations enable fitting and removal without tyre levers.

The most frequent problem I encounter is a puncture. I believe this is true for us all. In 50,000km of cycling over the last half a dozen years I've only ever seen one rider with a broken gear cable. I've never encountered a rider with a broken brake cable. I've broken a seat rail while touring due to my own poor handling (lifting laden bike by seat) and I've had a derailleur pulley fail on the same tour. My point is not that these things don't happen, just that they are quite few and far between. That doesn't help if it happens, but you need to evaluate the risk versus what would be necessary to make the repair, and whether you would be able to make the repair. Find a balance for the riding you do, prepare for the eventualities you can, keep your bike well checked and maintained and leave the rest to take care of itself.

In short, I think:

1. Punctures and related issues come first.
2. Adjustments/tightening loose things probably come second.
3. Mechanical failures including spokes probably come third.

So what's in my toolkit?

Punctures and Such

• A reliable pump than can easily deliver normal riding pressures. The Topeak Road Morph G weighs 200g without bracket, has an adequate pressure guage, and has a mini floor pump layout that easily delivers 140psi without stressing valve stems. Its O-rings are replaceable and it is easily disassembled for the odd clean and lube. I wouldn't travel without a pressure guage. If your tyre is meant to be at 105psi, run it at 105, and not some random pressure determined by your thumb. Thumbs just aren't that accurate :-)
  See http://www.topeak.com/products/Mini-Pumps/RoadMorphG
• A plastic tyre lever with a spoke hook and an abrasive patch for preparing a tube for a puncture repair. You are trying to remove the mold release coating on the tube, not necessarily abrade the tube, though in practice there might be little difference.
• Two spare tubes. Carry well packed in a plastic bag or similar to prevent wear from abrasion. In the past I've pulled a new tube from my kit prepunctured with a friction hole. Decide on how to identify a punctured tube, whether by using a coloured rubber band, or by tying a knot in the punctured tube. Whatever works for you to make sure you don't accidentally refit it before you've patched it !!
• C-Cure rubber patches. I like these minimalist and very flexible and reliable patches. Two small tubes of rubber solution. I always like to have an unopened tube available.
• Another lighter option is self-adhesive patches such as the Park Tools Super Patch Kit or a similar product. No rubber solution, everything you need in a tiny plastic container.
  See http://www.parktool.com/products/detail.asp?cat=17&item=GP-2
• Because I was foolish enough to import a bike from Moldavia with a rare tyre size, I also carry a folding spare tyre.
• If you don't feel a spare tyre is necessary, I recommend carrying a tyre boot made by cutting a small length from one of your worn out tyres. Alternatively or additionally, Park Tools have self-adhesive patches for temporary tyre repair called Tire Boots. A piece of old tyre and the Park Tools "Tire Boots" weigh only a few grams but should enable you to get home on anything but the most extremely damaged tyre.
  See http://www.parktool.com/products/detail.asp?cat=17&item=TB-2
• Presta to Schraeder adapter. I have Presta valve tubes. This tiny item means I have access to another rider's pump or a garage air hose should my pump happen to fail. It's tiny, takes no space, weighs nothing so why not.
• My Velocity Rims have plugs instead of rim tape. I carry a couple of spares in case I inadvertently knock one out during a puncture repair. While these items are very low risk, they weigh very little, take up little space, so there's no significant cost to including them.
• If you don't have quick release wheels, you will need a spanner to undo wheel nuts. Quite often front and rear wheels have different nut sizes such as 14mm front and 15mm rear. Check now. Rather than trying to undo and redo wheel nuts with a minimalist spanner, buy a real spanner. For example, A very elegant Stahlwille Stabil 14/15mm ring spanner at 55g. See http://tinyurl.com/4nr6wd
• What else is there to undo to repair a puncture on your bike? A chain guard, a brake reaction arm, whatever else there is, be sure to have the necessary tools.
  

These items represent 99% of the repair work I've ever had to do on my bike, and I suspect the same will be true for you.

Adjustments and Loose Things

I carry hex keys and spanners to fit everything I'm willing to touch on the bike.

• Teng Tools hex ratchet and 8mm spanner combination. I believe this is better and lighter than a multi-tool which often has many bits and bobs irrelevant to your bike. It's also a well made tool and with a reversible ratchet, it's a pleasure to use.
  See http://www.teng.co.uk/1400b-tengtools-mini-bits-ratchet_488_pd.asp
• Quality hex bits for each of the hex bolts/screws on my bike in a plastic hex holder. 
  See http://tinyurl.com/3f8vd3
• Stahlwille Stabil 8mm/10mm combination ring spanner for the nuts on my bike. It's another really nice tool at just 18g. You may only have nuts to deal with if your bike is fitted with mudguards, or racks or other accessories. Worth checking.
  See http://tinyurl.com/4nr6wd
• Signet S34295 hex bit holder for a 10mm spanner. Another hex bit tool. I need two for a couple of nut and bolt combinations on my bike. You might not. However, for example, some adjustable angle headstems need a hex key each side.
• A range of cable ties. Good for many a loose thing :-)
• Some rubber bands cut from old tubes for wrapping around things, stopping rattles, shooting at fellow riders at rest points :-)

Just to put some of that in perspective, the Stahlwille 8/10mm spanner, Signet hex bit adaptor, and 2, 2.5, 3, 4, 5, 6 and 8 mm hex bits in a plastic holder total 75g!! They provide a tool set of superb quality. The only disadvantage compared to a multi-tool is that the separate bits are more susceptible to loss. Leave out the 2, 2.5 and 8mm bits and it's only 50g!! Compare with the Topeak Mini 6 at 58g. I'm not touting weight saving, rather the quality and functionality of tools you can have for no disadvantage.

You might also look at the innovative Topeak Tool Bar

See http://www.topeak.com/products/Tools/ToolBar

and the Topeak Ratchet Rocket (compare with Teng Tools ratchet above)

 http://www.topeak.com/products/Tools/RatchetRocket

Mechanical Failures Including Spokes

The tools from the previous section are the tools you might use for repairs. In addition consider:

• FiberFix Emergency Spoke. This is a spoke made from aramid fiber cord (Kevlar) which can be used to replace a broken spoke of any length. It is compact, easy to carry, and more importantly, you can replace a spoke on the cassette side of your rear wheel without removing the cassette! Contains an adequate spoke spanner!
  See http://www.peterwhitecycles.com/fiberfix.htm
• J S Stein cassette cracker or Unior cassette cracker. Both these tiny tools are not much bigger than a spoke key and enable you to undo the cassette locknut and remove your cassette. Necessary to replace a cassette side spoke with a conventional spoke. I have a symmetrically built rear wheel with no dish to considerably reduce the possibility of any spoke failures, drive side in particular. I rely on the FiberFix Spoke.
  See http://www.sheldonbrown.com/harris/tools/cassette.html
• Chain breaker. Enables you to repair a broken chain by shortening it. Enables you to bypass a failed derailleur by shortening the chain. There are quite a few standalone lightweight chain breaking tools available, and there are quite a few included in multi-tools. The one I like most for lightness and function is the separate chain breaker that comes with the Topeak Alien XS multi-tool. However, it's not available separately which makes it quite expensive!
  See http://www.topeak.com/products/Tools/ALiEN_XS or
  http://www.parktool.com/products/detail.asp?cat=5&item=CT-5
• Spare chain Joining links such as the SRAM PowerLink or Connex Link. Enables you to rejoin your chain more easily. These weigh nothing and take up almost no space.
  See http://www.connexchain.com/Verschluesse/Connex-link/0_309.html
• Chain hook. To hold the chain while you break or join it. A bent piece of old spoke will do the trick, weighs nothing, takes almost zero space.
• Spare rear brake cable, and spare rear gear cable. These weigh little and while the risk of failure is low, the cost to carry is equally low, so why not? If you really want to be tight, just carry a rear gear cable. It'll work in either front or rear. If a rear brake cable fails, you still have all your emergency braking power. If a front brake cable fails, replace it with the rear.
• A small selection of nuts and bolts for things that could go missing during transport/assembly/disassembly. Just cheap insurance for a few grams. This might be more important for bikes fitted with racks and clamp on accessories.

How will you carry your tools?

If you have a multi-tool that does it all for you, then you can probably drop it in a jersey pocket or your seat bag. If your toolkit comprises several items, then you probably want something in which to hold them. I use the Ground Effects zip pouch because it was the only thing I could find. It's OK and has served me well for a few years.
See http://www.groundeffect.co.nz/product-detail-PAD-BAG.htm

If I had the time, I'd make a small tool roll with pockets for every little bit, and the traditional string tie. When rolled out it's somewhere to rest your tools, the empty spaces show if anything is missing, and the roll and tie stops anything rattling.

Among many, here are a few how-to articles:

• Park Tools http://www.parktool.com/repair/readhowto.asp?id=25
• Bicycle Tutor http://bicycletutor.com/
• Bicycling Fixit http://www.bicycling.com/channel/0,6609,s1-5-0-0-0,00.html
• Jim Langley http://www.jimlangley.net/wrench/wrench.html