Now you have me thinking about small hydro storage again.

Here is a guy's system that uses a 55 gal drum on his roof. He fills it using a solar panel and has a custom Pelton wheel driven generator to light an LED. The amount of energy stored is about the same as a AA battery. Your light could go for a long time on one drum of water. Maybe you could fill a bag of water, pull it up into a tree and get some light for an entire evening.
https://www.youtube.com/watch?v=CMR9z9Xr8GM