A science fair project does not have to be complicated. There are many experiements out there but it has to be fun not just an assignment. Here are a few items that Examples: scissors (blades act as paired wedges), door wedge, ax, wood chisel. xplain wheel, axel, wedge:Examples of pulleys in action: stage curtain, elevator, outdoor clothesline: Examples: steering wheel, faucet, wrench tightening a bolt, bike wheels, water wheel.

Sometimes just collecting together materials that can be used will trigger some ideas.  

For wheels, empty thread spools, screw-off soda or water bottle caps, scotch tape rolls, plastic lids from coffee cans.  Or go the the hardware store and buy some fender washers - they're inexpensive.

For axles: pencils, straws, skewers, a cut off piece of a wire coat hanger.

You can make a crank from a bent piece of coat hanger wire.

You can make ramps for marbles by slicing an empty paper towel roll in half lengthwise.

Here's where to get some inspiration:  Do a web search on "Rube Goldberg" and look at the images that the search engine finds.  These things are filled with compound machines - probably more than you can ever imagine.  Find some piece of one that you think you can construct from the stuff you've collected.