Cavernous only begins to describe the REI XX Large REI Nylon Duffel Bag, which swallows up 9,150 cu. in. worth of gear, clothing or whatever else you can fit in it, and comes with its own stuff sack.
420-denier ripstop nylon is lightweight and tough; dual zippers facilitate easy access into main compartment
The REI XX Large REI Nylon Duffel Bag has a convenient storage sack that doubles as a toiletry bag