Halogen headlight (for backup)
LED helmet mounted light (mainly for repairs)
2 LED blinkies
In seat bag:
Spare tubeI bought individual tools instead of a multitool because I wanted to have top quality tools for work at home, as well as on the road. A good multitool would replace a lot of what I carry, but it just hasn't made it into the budget, yet.
8 and 10mm ratchets
Small, 10mm cresent wrench
Spare chain link
Metric allen wrench set
Health insurance card
Spare AAA batteries for LED's
Electrical tape wrapped around ratchet
In my saddlebags, I carry my wallet, work clothes, and lunch (I keep shoes at the office). I don't carry a lock because I keep my bike in a closet at work. If I have an unfixable problem to or from work, I can put my bike on the bus. In the winter, I also stick an emergency blanket in the saddlebags.
At work, I keep energy drink mix and drip lube. Sometimes I need the sugar boost to get home at the end of the day. Sometimes my chain has an annoying squeek I don't want to hear on the way home.