It seems so small and insignificant, yet it's so important. The BB30 Wave Spring Washer is the keystone in your bottom bracket assembly, providing compression for proper setup and bearing preload, while helping to maintain adjustment after it's dialed in just right. They're also quite easy to lose or damage, so grab a few while you're at it.
Snap rings are pretty ingenious, except they love to launch in an impossible-to-track direction when removing or installing. Maybe you should keep a spare set of these BB30 Inner Snap Rings, just in case.
Tight tolerances and precise torque specs mean precision parts like this MegaExo 12 Left Arm Crank Bolt need to be replaced from time to time. Make sure the heart of your drivetrain is secure, and pick up a spare or two today.
A Quick Release Chain Link might have the greatest value-to-weight ratio of any Item in your toolkit. Keeping some stashed on every bike and in every kit is a no-brainer. FSA has you covered with 8-packs to cover your needs.