I'm picking up an old rigid mid-90's mountain bike (a Giant Iguana) for use as a commuter and beater bike on Tuesday, and I'll be picking up all the stuff I need for it after that.
Okay, what do I need? Since it's a commuter/beater, I don't want to put anything super nice on it, but I want the stuff to last. (Oh, and I'll be in desert-land for most of my time with this bike, so I doubt I'll need fenders.) I'll be using it to commute to school, possibly light grocery runs, study breaks at the coffee place, that sort of thing.

Given: New saddle, probably new chain.

Must-haves: Rack (it does have eyelets), lights (suggestions for bright-but-inexpensive ones?), flat kit for this bike (how to stow it?)

Probably: Second bottle cage, wheel reflectors

Maybe: Pannier(s) of some kind, very basic computer (that I'll store with me).

Any suggestions? Other stuff I should get that I haven't thought of.