I love crafts, and I think they are a great way to get kids to work together, at least side by side, if not on the same project.
You already mentioned painting and drawing and those are good, but I wonder if you can add some other projects they might be able to work on "together"? Like maybe your younger child could be decoraiting a bag to use as a puppet, while your older child could be using the same supplies to make a picture frame or a more complicated drawing?
Here's a great site with craft ideas for every holiday and lots of other themes:
http://www.enchantedlearning.com/crafts/
Hope this helps!