A few simple activities that can be done in the hut for the DIY Activity Badge
Have a few different light-fittings (strip light, bayonet, screw-in) and demonstrate/get older scouts to demonstrate them.
Show the scouts your hut's main breaker board, pointing out the master breaker and the individual circuits. Can explain how they're differently rated, so heating circuits take more power than lighting and therefore need a higher rated fuse. Talk about water and gas isolation valves/taps as well, ideally demonstrating.
Changing a plug:
You'll need some wire, a few plugs, flat-head screwdrivers, and penknives/knives/pliers for cutting/stripping the wire.
Unblocking the sink:
Can talk about chemicals that do it, plungers, and then take apart a U-bend from under a sink.