i got this idea from our church nursery. just save your 1/2 gallon and quart milk/juice containers. cut off the tops, clean well and put two together (one inside the other) so that there is no opening. there you have it...big building blocks. start saving now and in no time you'll have a enough for a fort!
heres a picture
heres a picture






we've made these in the past and covered them with the brick-looking contact paper, so they looked like bricks