Five mile each way commute:
Frame Pump
Spare tube and patch kit and multitool (small wedge under seat)
In Wald folding baskets (use spider web bungee cord to keep things in)
Cable lock
work shoes (I wear spd fo the commute)
Laptop (some times) in it's padded case
Lunch (sometimes)
Kids back pack (sometimes when we commute to school/work toegether)
shorts/shirt (sometimes if I plan on a long ride home)
On way home....groceries/stuff from hardware store/books if I hit the library.
__________________
Life is too short not to ride the best bike you have, as much as you can.