continuing the theme of filling up the area, you cold try things like:
balloons, bouncy balls, unbuttered popcorn, etc...
if you are not in the mood to fill things up, then depending on the type of stuff in their work area, you could go about turning everything upside down, backwards, or inside out depending...
covering in post it notes is fairly decent, though time consuming.
seran wrap is pretty good too.
filling up a cube wth peanuts is hilarious but would probably actually be rather expensive on you.