I purchesed the largest RKA tank bag available (it is expandable) along with the RKA pannier and top box liners. The TB has a number of external zippered pockets, two zippered main compartments, map case and rain cover. It also has a provision for wiring a power outlet into the main compartment from the front or rear. Three point mounting allows refueling by releasing a single snap, tilt the bag forward for gas cap access. Fueling can be accomplished without ever dismounting. Love mine.