Hmm... you could paint a wall with magnetic whiteboard paint, and then get one of those packs of 100 magnetic whiteboard cards - write on the wall if you want,

Hmm... you could paint a wall with magnetic whiteboard paint, and then get one of those packs of 100 magnetic whiteboard cards - write on the wall if you want, and then write on the cards too - erase the cards if you want, or just lift them off and move them around... I might do that.