I think that some dollar stores have Solar Lights for a buck or two.  I'm not sure how to get them in plastic water bottles but that is a clever idea.  You just need to ensure that they get "charged" up.  One bad thing about solar lights is that the wiring must be soldered using some cheap or cold solder methods as I had to repair our fiirst few. 

For camping, my dad had what he called a "carbide light."  MAN that thing was BRIGHT!  Turned night into day, in an albeit small area.