My wife used the gerber bags while she was breastfeeding our son. they worked ok, but they had closure issues...we had a few come open when they shouldn't have, they also we not very condusive to freezing. I keep some just for outdoor use. If you're going camping, the water idea works well, as well as keeping individual portions of food to fix later. I've used them for to keep everything from trail mix to a marinated chicken breast. As I said, the gerber bags are ok, but check out bags by medela, they're a tougher plastic and can stand more re-uses, just wash them out and go again.
Another use is to fill them with water and freeze them, put them in a cooler to keep perishable stuff cold, and you've got potable water when they thaw.