My "go to" site is http://www.basegear.com/

They have the best prices overall that I have found online and there are sales going on various products all the time. My last order took less time to get here by mail than most letters take to get across town.

I think the things that are "best bang for your buck" would have to be things that serve multiple purposes. First thing that comes to mind for me is the AMK Heatsheet Emergency Blanket. I would also include something like aluminum foil and 550 Para Cord.