I love the spirit behind this idea in the book More Mudpies: 101 Alternatives to Television (great book, by the way)
"There is an Inventor's Box in our garage filled with the kind of junk most people love to get rid of. Two coffee cans, a bicycle chain, an old eggbeater, and a broken thermostat from the newly repaired furnace are the latest additions. The box is used year-round and has generated everything from doll furniture to intricate contraptions that magnetically close doors.
You may have similar inventions ingredients (disguised as junk) in drawers and under beds but not collected together and called an "Inventor's Box." That's the secret. By placing the items into our box, the rules of function are eliminated and the bits can be reinvented into something new. Children, with their unburdened perspective, are naturally equipped to discover new uses for familiar objects.
When you clean out the garage and junk drawers to create your Inventor's Box, keep in mind that almost everything has potential for invention. Grand ideas are hidden in the pieces of an old game, the innards of small appliances, cat food cans, and rubber bands...
The act of creating cultivates creativity in children, not the creation itself. Our spirited four year old reminds me of this often. He thinks invention and adventure are the same word. "This is for my wire adventure," he declares one day, holding up a trio of rusty coils. And, of course, he is right."