Built a batch of these for an outdoor school. Fold up compactly in the boat until you need to move gear up the beach or overland between lakes. Very sturdy of 420 Denier Nylon Packcloth. 2″ webbing shoulder straps. Handles on top and bottom. Over 3300 cubic inches in capacity.
I can build some for your School. As little as $40 in quantity.
Portage Pack
Oware 