I've been using a platypus big zip in packs with hydration bladder pockets, and have also simply laid it on top of the stuff in the pack. Eventually the thing might start to leak, but I've had it jammed in behind a bear canister many times, yanked it out and stuffed it back into full packs, and still have the same one - the blue ink is wearing off the plastic but it still zips securely and doesn't leak despite my less-than-delicate use after three years.