I use cleaned out plastic milk jugs a bunch. Refreeze and reuse, less water in cooler. If I run low on water, I been known to drink it. But if wanting to keep ice for a week or longer, I usually buy blocks, pack them tight and put a bit of dry ice in the cooler. For the few times a year I need to keep ice a week or so, I buy blocks, I don't mind buying them as I lack the patience to use a mold weeks in advance.