Individual achievement, self-improvement and self-reliance are foundational values of mountain biking. Following this ideology, mountain bike races are completely self-supported. Outside help is not allowed. No pit repairs, no spare wheels, no hand-ups. So if something goes wrong with your bike, its on-you to get it going again.
No Tools, No Problem? You can save some weight and have fewer loose bits to worry about if you leave the tool kit behind for the race. The obvious downside is that you won’t be able to fix your bike if something goes wrong. For races with shorter laps you have a better chance of being able to hoof it back to your car to commence a fix. This decision depends on your level of confidence in your equipment or your mechanical ability, but really, it comes down to how you judge the risk of a mechanical mishap taking you out of the race and how important finishing is to you. Your call.
A flat tire is the most common problem, even with modern tubeless systems. A spare tube will fix this in short-order. So, the most bare-bones (and seemingly most common) tool kit combination includes a spare tube and a CO2 cartridge and inflator. Some folk simply duct tape these to the bike, on the seatpost or elsewhere, other people keep it all together in a plastic bag or tool wrap (recommended). Personally, I find that a plug kit like the expensive, but fast and effective Dynaplug Racer will almost-always patch a hole that is too big for sealant. So I might recommend something like this plus a CO2 as a great minimalist kit.
The second most likely thing to disable a bike is a broken chain. So leveling-up your tool kit means bringing a multitool that includes a chain tool. The Allen wrenches and other bits can also be useful if a handlebar or saddle get out-of-whack as the result of a crash. Before you buy a multi-tool, make sure the bits it has matches all of the bolts and screws on your bike. If you’re ‘in it to finish’, a tube, a way to inflate it, and a multitool with a chain tool and other bits will almost certainly have what you need to get you there.
Don’t worry about what you can’t prevent. A lot of other things can break especially as the result of a crash: derailleur hangers get bent, cleats get torn out of shoes, rotors get bent, spokes break, etc. For a lot of these problems, you and your bike won’t be performing optimally, but you can usually ride it out. Sometimes, random mechanicals that you would never expect take you out of the race. Usually those things will at least make for a good story.
For an endurance event, especially a point-to-point race, you’ll probably want some spare parts and repair supplies to fix these unexpected issues. Here is what I carry for long events and ‘epic’ rides:
- multi-tool with chain tool (a chain tool can also be used as a valve core remover)
- pump and CO2 inflator with one cartridge
- tire lever
- spare tube
- spare valve core (the whole presta valve is not needed, usually its some part of the core that fails)
- spare derailleur hanger (these are fragile and without them your bike can be crippled)
- spare cleat bolt (might be useful somewhere other than your shoe)
- spare tire plugs
- two band aids (apply at first sign of nipple chafing)
- shammy cream (apply at first sign of tant chafing)
- safety pins
- ibuprofen (aka Vitamin I)
- bit-o’ toilet paper (has literally saved my butt on a few occasions)
- 3-4 cable ties
- 2-3' of duct tape (wrapped around pump).