Here are some of the essentials and some recommended items to keep on your bike.
Tool Bag – Big or small, it’s up to you. Pick one that can carry your tools and possibly your car keys, phone, or wallet.
Spare Tube – Do you want to walk home? Pack a spare tube.
Tire Levers – Some guys take care of this with their muscular fingers. These make it easier.
CO2 Inflator and Cartridge – A pump is nice, but when you have a flat 80 miles into a 100 mile ride, this is much better.
Allen Wrenches – Almost everything on your bike can be tightened up using an Allen wrench (or hex key). At a minimum, you need a 4, 5, and 6 mm, but a 3 mm and an 8 mm are handy at times.
Small Screwdrivers – What cannot be tightened or adjusted with an Allen wrench can probably be tightened with a screwdriver. Note that some multi-tools will have hex keys, screwdrivers, and possibly other tools in the same bundle.
Optional, but really good to have:
Tire Patch Kit – When you ride through broken glass, is it possible to get a flat on both the front and rear?
2nd Spare Tube – See tire patch kit above.
Pump - After all of those flat tires, you might be out of CO2 cartridges.
Dollar Bills – Lots of uses for these. Emergency Gatorade and roadside strip clubs notwithstanding, you can use a dollar bill to line the inside of your tire if you cut a gash in it. This will prevent the tube from protruding through the tire and allow you to make it home.
Chain Tool – Sometimes your chain breaks. Not often, but it can happen. This is a small tool that will allow you to put your chain back together again and finish a ride. When you’re 20 miles into a 112 mile Ironman leg, you don’t want to DNF because of a broken chain.
Chain Links – Use with chain tool for an even faster chain repair.
Spoke Wrench – If a spoke loosens and causes your wheel to wobble, you can fix it enough to get you home.
Spare Spokes or Fiber Spoke – Replace a spoke while you’re on the road? It can be done if you have the tools and knowledge.
Cell Phone – And the number of a good friend who will drag themselves out and haul your sorry butt home when all else fails.