another thing you can do with something common to many households, beer. My friend and co-worker Sullivan turned me on to this. It's her art, not mine, i just thought i'd post the idea.
a half rack of beer
innate artistic ability (or the desire to "spruce up the place a bit" without prostituting your art.)
bag (i suggest paper grocery, that way you can keep these in one while keeping stencil in other...but that's another project.)
Step 1: Get an Empty Beer Can. Tall Boys Are Better But Anything Works.
Make sure to get the top and bottoms to fold on the same side, resulting in a fairly smooth side and a crappy side.