About a month ago I was on an 8 day backpacking trip through Shenandoah National Park. I'd arranged to have a friend meet me for re-supply halfway through. Unfortunately, I'd fallen in with a fast crowd and was 27 miles past where we'd arranged to meet. Fortunately, I was carrying my cell phone, which typically has about a week of standby time. Unfortunately, away from civilization the signal is much weaker, so unbeknownst to me I only had about a day and a half of standby in this case. I found this out on day three. I began thinking about backpackable solar charging solutions. I did manage to yogi a cell phone and get ahold of her, but in a less busy park things might have gotten really out of hand.
I'd had fantastic weather until day six, when I got hit with real backpacking weather: thunderstorms and cold, driving rain. When I got home, my digi-cam had water damage. It mostly works, but sometimes won't turn on or turn off now, and the LCD has cloudy water spots, this despite being inside a ziplock bag inside my pack. I began thinking about lightweight waterproof electronics enclosures.
Then, I started thinking "Hey, I can do both at the same time!" Nine prototypes later, this is what I had, the "Rain or Shine Solar Charger." In addition to being useful for backpacking, this charger attaches with parachute buckles, so you could attach it to a messenger bag, or a bookbag, or hang it in your kitchen window. It takes about ten hours to charge a typical cell phone, but it's a storage charger, so you could leave the charger in the sun to collect energy during the day, then plug the cell hone in at night to charge from the stored energy.
This is a fairly complicated project, which will likely stretch either your sewing skills or your electronics skills, but the results are well worth it.
If you'd rather skip all that and simply purchase this one, the Etsy link is http://www.etsy.com/view_listing.php?listing_id=6464822