I carry 2 tubes co2 and a mini pump, multitool with a chain breaker and spoke wrench. I prefer overkill to being stuck far from home and needing to rely on someone to pick me up. I once helped, what must have been a new rider, change a front tire flat. He had nothing, at all, and it was maybe 10 min. before dark.

My stupid tip: After using a co2 cartridge, use it to cool yourself down. Just maybe don't put it on exposed skin. It really doesnt do much but maybe the placebo effect will make you forget about the troubles of getting a flat and motivate you to keep going hard.