Tube, patch kit, tire levers, co2 pump, 6 co2 cartridges, Wrapper from powerbar or like for tire patching, Park multi-tool, chain repair tool, extra chain link, ID, mini plier for my disc pad retainers, a little money.

I think that's it.

Knowing how to use the stuff is important too. Can't count the number of times I've stopped to help some poor frustrated soul figure out a new pump or fix a flat. Not that I mind helping (sure don't) but sometimes they've been there quite awhile before I come by. Oh, and if you've got a tube kicking around in there you might want to protect it with something, sometimes they get holes rubbed into them while they're in a seat bag.