Water Bags

If you or someone you know drinks wine, purchase some in the boxes.  The plastic pouches are very tough and can be reused as water bags.  Just rinse out well with baking soda water (a couple of times) and sew up a nylon cover to go over it.  Leave a hole for the spout to slip through, and add carrying handles at the top, also used to hang it for regular use.  They are very light and fold down to almost nothing when empty.