My observations about toolkits:
1. BY FAR, the most common failure point is tires. You need to have this covered and have everything you need to remove the wheels.
2. Next up is electrical failures: dead battery, blown fuses, loose connections, shorts, etc. You need a small multi-meter to be able to diagnose most electrical problems.
3. Next up is crash damage. I carry several ways to jury-rig the bike back together. I also carry temporary tie down straps to allow me to get the bike onto a trailer or pickup if needed which can also be used as a tow strap.
4. You're much more likely to have some fiddly problem with something minor than to have major mechanical issues. You generally aren't going to need big/major tools to do engine overhauls or major bike disassembly. If something major fails, you're probably going to truck it someplace or get it home anyway. You do need lots of fiddly tools to get to small things such as needlenose pliers, stubby screwdrivers, pointy instruments, sharp tools, etc.
5. Carry spares: bolts, screws, fuses, cables, chain, etc.
6. Carry jury-rigging stuff: qwik steel, epoxy, shoe goo, tape, tie-wraps, hose clamps, bailing wire, etc.
7. Carry the stock toolkit - it usually has some things that are machine-specific.
8. MOST IMPORTANT OF ALL TOOLS: bottle opener and corkscrew.
- Mark