One of my favorite repurposed items is our magnet board - really an oil drip pan from the discount store. We use it a lot for all kinds of magnet play. But we've also used it for other kinds of play. Most recently we added sticky paper (clear contact plastic, sticky side out).
You could use just about anything to put on the sticky paper. I'd recommend foam, plastic, or wooden items so kids could put them on and take them off. We used foam cubes (purchased from the dollar shelves at Target a few months ago) and small wooden blocks (on sale at a toy store). You want something that is light enough to stay on the paper.
The kids experimented with designs and just putting things on the paper.
We even had a car "stick around," too. A boy tried putting it on wheels-side to the paper, but it wouldn't stay. So he flipped it over to stick on.
Kids came and went with this activity. At times the paper would be cleared and new designs would emerge.
I did have a boy try to stick blocks in areas above the paper, so kids need to know boundaries. I like to use colored masking tape so kids can easily see where the sticky paper is. Or you could use regular contact plastic that is white and not clear, so kids will know where to place the items.
(You can see more sticky paper and blocks at Brick by Brick.)
Full disclosure: I copped this idea from Deborah at Teach Preschool. Her blog is great and I'd recommend it to anyone who has anything to do with young children. Read it!