I participate in a lot of demonstrations for which I need to mass-produce armbands or banners, sometimes at a moment's notice. Cardboard, an X-acto knife and spray paint are all you need to create easy stencils that will last for a while.
I'm putting this up here just as an example of art you can make from discarded materials. Red Bull actually has an "Art of Can" art competition in which artists make some pretty amazing sculptures using these soda cans. Start drinking, then start creating!
