The idea of using turbines to create energy is a whole business but it’s not, generally, one that’s fit for the portable market. Well, that’s true of most of them but not the Waterlily Turbine, the USB charger that runs on water power.
This is a portable water wheel that you can throw in your gear bag whenever you head out. When you’re in need of power, just throw it into some running water and it can power up whatever you need that charges via USB. Downside, you have to have your electronics pretty near water. Which isn’t great but there’s a ten foot cord so, you know, good luck.
This also works with wind. Just hang it up and it goes. I suppose you could also just spin it really fast with your finger if push comes to shove. Anyway, portable renewable energy,whenever you need it. You can get this for $199.