I always carry a small supply of the wonder substance dihydrogen monoxide (i.e. water), but my pocket/stealth EDC doesn’t allow for more than about a 1-ounce bottle. I’d like some kind of flat water pouch that I can keep in a back pocket with 2 or 3 ounces always in it, and that I could top off to (say) 8+ ounces for hand-carry if needed. I’ve tried a couple brands of breastmilk storage bags, but even with their double zip-lock seals and allegedly sturdy construction, they slightly but readily leak when riding in a back pocket. I can’t believe this isn’t a solved problem.