I just ordered one of the Goal Zero solar charging kits. I like that it will charge AA batteries or my cell phone directly via USB port. Smart phones are very power hungry beasts; keeping them up and running using solar is probably a good thing.

FWIW, On my S3, I found "assistive light" under the "widgets" section in my list Applications and widgets. There is no corresponding App listed in the App section. Real simple; touch the widget, light on, touch again, light off.

Note; I am new (2 months) to smartphones; there seem to be lots of useful things you can do, most of which are undocumented and if you do find them, no "user guide" on how to make them work. Lots of experimentation is in order.

quite a few nice mapping apps in this thread:
http://www.expeditionportal.com/forum/threads/68418-Overlanding-Phone-Apps

tons of first aid apps listed here:
http://appcrawlr.com/ios-apps/best-apps-first-aid-information

Note: I'm not affiliated with the above, just passing the link.

Just recently got my first smart-phone, Samsung Galaxy Note II.
After playing around I found out that it drains battery within 24h when heavily using internet or gps or other functions.

So now on the way by mail is coming a Samsung portable battery pack with 9000mAh. That will let me charge the phone 1-2 times. http://1.androidauthority.com/wp-content/uploads/2012/09/Samsung-battery-galaxy-s3.jpg

A Goal Zero solar charging kit available through Amazon and other places online will let you charge and recharge your phone indefinitely while away from wall power or during electricity blackouts. All you need is sun. Nice in that it charges AA NiMH batteries and uses the batteries as a voltage regulator to allow charging smartphones (which can be finicky regarding charging voltage.

Not affiliated with Goal Zero or Amazon, but I have the unit linked above.

I just spent the last week at summer camp with my Boy Scout troop, and tried my Goal Zero charger, but we had no sun!!! It rained every day. There was no more than a couple of hours of sun on any day. I got almost no usable charge from that on my phone. I did not need the phone, I was just trying to see how the charger would do. It worlds, you just need ample time in the sun.

I've used http://www.verbatim.com/prod/accessories/power-pack-chargers/aa-power-pack/ on two scout camp outs and when the power was out last week. A few of eneloops in the backpack works fine.