I bought a carton of 4 oz. water packets a while back. They're O.K., but I've had a few leak into my daypack, and they're a bit difficult to open and use. Does anyone have any experience with Aqua Blox? It's a 'juice box' size purified water container with a straw. Specifically, any experience with keeping them in a car, where they freeze and thaw numerous times over a winter.