Yeah, something like that. I could see one with quick attach buckles that could mount to a pack and if not on your pack, could mount to a bino harness for short hikes.
Has anyone seen a water bladder bag that can attach to the back or side of a pack. An add on bag on the outside of the main bag seems like it might work well. Easy to get to, won’t soak your stuff if it fails and can be removed if not used. Thoughts?