Our electric circuit lessons have come this: the making of flashlights. They're probably not something you'd want to carry through the dark forest during a heavy rainstorm, but they do work. I try to designate some specific requirements for the flashlights: I like for them to be durable enough to withstand a basic shake test, and I like for the "guts" to be fully enclosed in the "case" of the structure. The switch has to work, too.
The biggest struggle for the teams seemed to be trying to figure out how to include a switch in the system. While we built a basic series circuit with a switch, the day before, some groups wanted to use a parallel circuit for their flashlights. For the longest time, the switch seemed to make no difference: the light would not turn off. Finally, they figured out the switch had to go between the battery and the light bulb. Enclosing the system in a paper case was also a challenge.
