I used to until losing it recently. It was an Altoids tin that held some first aid stuff, "repair" stuff, and few odds/ends.

First aid: aspirin, Imodium AD, Midol (for the wife), Benadryl, bandaids, moleskin.

Repair stuff: duct tape, dental floss, zip ties, safety pins, sewing needles, small uber-strong magnet, paper clip

Odds/ends: small compass, mini-Bic, trick birthday candle (relights itself after blowing out), emory board, 3 NATO stom matches.

The theory behind this kit (coupled with my LM multitool) allowed me to make a lot of makeshift repairs to stuff or handle minor boo-boos right on the spot rather to go off in search of the necessary supplies. Most of my time is spent in urban setting where I am able easily able to obtain water, shelter, food from many places under most circumstances so I don't worry about that (though I do keep extra food/water/clothing stashed at work and in my truck).

It was really just a convienence kit and and I haven't replaced it in the six weeks since losing it, though I did start carrying a lighter. I like to know I can call up fire anytime I want.

Sidenote: my keychain has a whistle, a flashlight, a P-38 can opener, a pill fob, and a screwdriver thingy.

-Blast