Pump strapped to downtube, everything else in the saddlebag:

1 spare tube
co2 cartridge w/ pumphead I've yet to fully understand how to use
levers
patch kit (need to get a small square of sandpaper)
multi-tool
1-2 handi-wipes (swiped from a bbq restaurant)
travel-size tube of ibuprofen
maps of the bike trails I ride

Since I'm starting to ride longer distances, I'd like to carry a second tube. I tend to waffle back and forth between militant minimalism and carry-the-kitchen-sink paranoia. I'm considering getting a bigger Camelbak to be able to fit the extra tube and more food!