Wrap some baker's twine or other string around a wooden block to create a graphic textured stamp. -can also use rubber bands- Stamp on inside of paper bags from grocery store or paper that comes in mailed packages, use as wrapping paper.
Magnetic number fishing, they add what they catch! As well as addition, develops hand/eye coordination, fine motor--I love this for magnetic letter fishing too! When they catch a letter, they say its name and sound.