Paper (folded for cards)
Stamps (I would say already inked stamps are the way to go. First because then you don't have to have a constant battle with your toddler over who gets to hold the ink pad and second they don't ink all over little hands as easily)
Markers (only if you are brave!)
Pretty self explanatory. Usually if we color we only use crayons or stickers but for this we pulled out everything. My daughter was actually interested in it for a good hour, which I contribute to the variety of things she had to use. We made our cards for Dad and Grandparents.