Electrical outlets are few and far between when you're out in the wild, and lugging a generator into the jungle isn't always practical.
One nifty little alternative power source is the wind-up cell phone charger. Wind a small hand crank to create kinetic energy. Wind-up chargers store up kinetic energy and convert it usable power. Similarly, rechargeable kinetic batteries are under development. Design engineers Yeon Kyeong Hwang and Mieong Ho Kang have proposed a rechargeable AA battery design that uses a spring and a twisting action to charge a Ni-mH battery, and Brother is researching technology that would utilize a shaking action to recharge batteries [sources: Yankodesign, Samaniego].
Until kinetic rechargeable batteries become commercially available, you can invest in a battery or solar-powered USB charger. If you are so inclined, you can even make your own from a kit such as the MintyBoost. Before purchasing or building a battery powered USB charger, be sure to check whether it will work for the device you want to power.
Got another essential gadget for staying wired up when you're camping out? Be sure to let us know in the comments! Find an article on how wind-up chargers work, as well as other related HowStuffWorks.com articles, on the next page.