Stickers, lace, ribbon, heavy plastic jar lids - for tracing or holding paint, old parts from games, dried beans, rice, cinnamon sticks, alphabet macaroni - or any kind of pasta, bingo markers - great for making dots but can also be using for drawing, Q-tips, fabric squares, old shirt or apron to be worn during messy projects, painter's tape - easy for little hands to tear.
Check out your local $ Store(s) and resale shops. I find amazing things there!
Older children would probably enjoy searching for craft projects online.
Here is my favorite link for children's craft projects:
http://www.thecraftycrow.net/