With some scrap paper, you can create some really cool 3D works of art. Origami can cost you next to nothing to do and provide fun and next-to-free entertainment for your whole family.
There are a lot of really cool resources available such as such as Origami Instructions.com, where you can learn to fold origami birds to origami whales and everything in between. Origami Instructions even has a YouTube channel to help you master the art of origami.