You'd be amazed what you can do with a few cans! Check out this (courtesy of Journey into Unschooling).
Here are some magnificent solutions:
Zee crafted a cool knife.
Noah (7) and Aimee (10) made a "house-car" out of 3 soda cans, string, Scotch tape and colored paper. It was a great canstruction effort!
Orca and Alce just sent in some magnificent creations: a robot, a submarine and a waiter with a plate of potatoes! You can read more about these solutions and others here.