I thought I'd post a couple of examples of cards made in groups -- those below were made by two friends and me. Sorry they're so big, I'm still figuring out how to use the photo edit software so please pm me if you can help me shrink them more.
In the first bunch we each had certain materials that we could add onto cards as they went around the table, which led to:
Kitties Are Hiking
Kitty Has a Nightmare:
...and in these, we took turns quickly adding images made out of only a pair of dots, scissors, and black marker:
(The pictures above include an alien eye, tea & cookies viewed from above, peace broken & bleeding, a chocolate-covered cherry, a lava lamp, and an eight-ball.)