Originally Posted by ctyler
I ALWAYS ride with a spare tube, tire levers, patch kit in a seat bag. Changing a tube is so easy to do.
Carry all of this, plus get the kind of frame pump that has a flexible nozzle. It will save you on damaging the stem (inflexible minipumps are hell on stems). This should all fit in a seat bag. You should also carry the following:
A multi-purpose tool (or wrenches and screwdrivers to work key bolds and screws)
An energy bar (in case you break down)
A tire guage (to make sure you inflate to the right pressure)
A health insurance card and/or other ID
Cash and/or credit card
Don't let the list intimidate you. Ctlyer listed the critical stuff (he only left out the frame pump). If you get nothing else, get what you need to change a tube 15 miles from home.