craftgrrl | Crafts for 12 - 17yr olds

A friend of mine is a librarian and has asked me to come to her library a few times during the summer to do some craft programs with the kids. The theme of the programs is "Express Yourself!". I need to come up with about 5-10 low-cost crafts that can be done with a small group (10-15) of kids between the ages of 12 and 17. I've come up with a few ideas and they don't have to connect back to books or anything. They just have to fit with the theme and be fun for the 12 - 17 crowd.

So far, I'm thinking of:
-Decorating drawstring backpacks or ID pouches from oriental trading
-Carving a "personal stamp"/lino-cut type stamp out of styrofoam packaging and printing a set of note cards with the stamp

I'm just kind of drawing a blank for other stuff. The "classes" will be about 2 hours in length, so I could do either one or two crafts depending on the time they take. Also, they need to be "one size fits all" kinds of crafts, since I'm supplying all the materials and have no way of knowing what size the kids are. So... help! :)