Originally Posted by NoRacer

I use one of these (Topeak Survival Kit):





In the bottom container, I have an extra tube, CO2 inflator, 1 box of 3 CO2 cartridges, spare batteries for my tail light, and some quarters in case my cell phone dies.

I use a CamelBak M.U.L.E. to carry a bike map, head light, harness, & battery, spare clothing, bike lock, cell phone, wallet, keys, and first aid kit. Sometimes there's still room for a tire--folding type of course.