Maths hat - make a hat or crown and put numbers or shapes on the front - the rest of the class gives clues so the wearer can guess what it is. Can be used for number bonds (image from activityvillage.co.uk).
Styrofoam, like the stuff from take away containers or from the grocery store, can be used to make your own stamps. (This site is in French. I tracked the photo to http://www.funnycrafts.us/printmaking-ideas-for-kids/, but there are no further instructions there. I guess they figured the pictures said it all.)