I use a Lowepro Nature Trekker for my RB67. In it I can fit:
One RB body, a 50mm, 90mm and 140mm lens, four 120 film backs, a short and long extension tube, lens hoods, various glass filters, a Lee filter system, a sekonic studio delux meter, cable release and a load of film. The tripod straps to the outside, and if I ever need to take anything else, it goes into Lowpro sliplock bags that attach to the outside. It's quite compact like that but HEAVY, though the bag works well for that kind of load.