Recently I bought myself a Utili-Key for about $12. I loved the idea, but after a week, it had fallen off many times, and there was no good way to modify/fix it to solve the problem. The feature I used the most was the knife blade (pretty much the only useful feature).
So I decided to make my own. I bought a blank LED style key from the hardware store for less than $4 w/tax, and filed down the top edge to be mildly sharp (use some common sense).
I've carried it on my key chain for a couple months now, with no holes in my pockets, cut fingers, etc., and used it to open boxes, mail, cut/strip wire, light my way in the dark (it's surprisingly bright), etc.
You could do this for less than $2 without the LED, but I figured I might as well have a 2-in-1 tool. Also, you might be able to cut out a bottle opener shape on the under side, or file the tip flat to have a screw driver?