Ah, memories. XTRA was originally Casino Express. They had 737-200adv and had a unique way to extend range. They did not accept checked baggage. You had to carry on all your bags. Each pax was allowed two carry ons. The only requirememt was the bag had to fit thru the scanner at the security checkpoint. Back then, the checkpoint scanners were large enough to fit bags that would normally be checked bags. These particular 737s featured either 118 or 122 coach seats, and overheads around the size of erj 145 bins. Made the jet seem much more roomy, but obviously the carry ons wont fit. So the ground handler would setup a belt loader at 1R, and send all the bags to the bins as the pax boarded. These bags were calculated at carry on weight. So you had a full 732 going CLE to RNO without a fuel stop. That was pretty slick.