We have a box that we keep on hand of toilet paper tubes, plastic containers from yogurt or whatever else and newspapers. Some of the things we make with this odd assortment of items is a marble run and paper mache. It is a great craft that allows us to use some of these items more than once before we throw them in the recycling.
www.tipnut.com has some great ideas for what and how to paper mache.
Also if you google homemade marble runs you will be amazed at some creations people make.