A wind-up shaver. Sounds absolutely perfect for someone like me who has always shaved with an electric razor - unfortunately the safety razors used to give me a terrible skin rash - and often goes to places where there isn't any electricity.
Of course, when you're in civilisation you can plug the razor in and charge it, either through a power point or via your laptop. But when you're beyond the black stump you just wind the handle to crank up the built-in generator and charge the battery.
Just to check how well it works I ran the battery absolutely flat and then cranked the handle for about a minute. That produced enough power to give myself a good shave.
As a further test I just took it on a week-long visit to Niue and it did the job perfectly. There was power, of course, but with just a few twirls of the generator a day I didn't need to plug it in at all.
The trimmer isn't actually much good but the razor itself gives an excellent shave. The Hand Crank Shaver is sold at nznature.co.nz, where right now it is on sale for $54.95.