Agree with deskjocky 100%. It wont carry weight as well as a “real” load hauling pack, but for lighter loads in a smaller footprint it may be better than the “real load carrying pack” for some—thats why I like them. That said, to me a 40l pack is an overnight size already unless you are talking midwinter conditions and gear. I have a popup 18 and 28 that I use as day packs, the 28 for really cold conditions. You can put plenty in the load shelf to add additional capacity, but imo an entire 40l pack behind a dry bag is going to eat up all of your meat-carrying ability for the trip home (unless you are assuming multiple trips), as well as you’ll have all of the stuff in the 40l pack an additional 8-10” behind your back, its going to carry like crap withbthat weight so far away from your center of gravity. So yes, it’ll work in a pinch, but Id pack differently if doing that, and its not ideal.