Regardless if you’re a prepper or avid camper, you might want to have your phone with you and have ways to actually use it when you’re away from a wall socket.
This is the first and easiest way, if you’re just going to be away a couple of days and might need an extra charge or 2. I use the HTC BB G600 myself which can store 6000 mAh (6Ah) which depending on phone gives you roughly two charges (it’s called “double charge”). The HTC BB G600 costs about $70 each but I’ve seen it for sale on ebay for about $35-40. This thing (or similar, there’s cheaper larger ones) I just prefer the HTC battery bank for the form factor, is just a MUST since it can be used with other things to “store” Ah.
This works pretty much anywhere you have decent about of sun/daylight. Up around the north pole now, you might want to get other solutions. There’s various variants on this, but most of them can charge to an internal battery which you then charge you phone from. Just be a bit careful with your phone if you got it hooked up directly to a solar charger since it can get toasty warm. You have a nice selection of solar chargers on Solio, bonus point is that you can power a water purifier with one. Around $100 or so. Can of course be used to charge an battery bank, or charge a couple of battery banks just to be on the safe side.
Bio-mass burner/camp stove
Yes, there’s camp stoves that you can charge your phone from. This is being done by an peltier element that creates an electrical current between the hot side the and “cold” side. There’s various makers of this, but the BioLite camp stove looks pretty cool. About $130 each. And you can cook dinner on it, or s’mores, while you charge your phone or your battery bank. Pretty clever little thing.
Hydroelectric generator and other means
This is perhaps a little more tricky, but not really hard if you invest a little bit of time and money. Same with wind turbine.
Hand cranked charger
This is of course the most basic ways it can be done, SOSReady got one of those. But, I’m sure there’s others around as well.