The following projects were developed from whatever was cheaply available. Others will probably not be able to make them exactly the same but these suggestions may help. The wheels on the 4wd car for example are milk bottle caps from a local fast food chain, but suitable similar things could be found almost anywhere. Encourage children to be resourceful. It’s much more fun to build something you dreamed up yourself than to throw together a kit set that somebody else designed.
water pipe flute http://www.markshep.com/flute/Pipe.html
Search Coil Magnetometer for detecting earthquake precursors
(Some project details still to be added)