I just ran across
this article, which is about a recurring theme in power generation. It's very easy to see that our economy is very power/energy-oriented. Without it, the great majority of us would be without a job.
Thus I think an energy-storage, potential energy (etc) type theme could be a good candidate. You can make a wind turbine out of crackerjacks (tower), haagen-das (base), and a soda can (propellor blades). Well ... you can
sort of make a wind turbine out of them...