Here's an idea I've always wanted to try out, but have so far been too lazy to do it... It requires some skill with Photoshop, and a bit of capital to invest to get it going:
Download some fairly high resolution images of video game characters, recognizable screenshots from the games, etc.. Anything from Mario or Zelda games are always popular. Run some filters on each image to make it look like either a sketch or watercolor painting, then have a few printed on heavy cardstock at Kinkos, Staples, Office Depot, etc.. Take a fine point black felt tip marker and sign each one.. write 6/15 (or some other fraction) on the back to make it seem like a limited edition series.
Put one of each in a binder or attach them to a display board, and have the rest in 9x12 envelopes.. I've seen similar prints sell for $20 each in my city, although I doubt those were just found images with a few filters applied to them.
Like I said, it requires a bit of capital up front but if there's a print shop nearby then you could start with just a few and then get more printed throughout the day if sales are good. You could collect emails for a draw for a larger print, free print, etc... lots of stuff you could do with that.