When I need to carry four panniers and a rear rack stuff off the tandem I enclose them all in a light weight duffle from Osprey packs called the Airporter. It is designed for enclosing a large backpack as checked baggage on a flight.Twelve ounces and 8000 cubic inches as I remember. I see at this link that the model I have has been redesigned & renamed. http://www.ospreypacks.com/Packs/Sid...s/AirporterLZ/

With the shoulder strap I can carry the bike bags and handle the tandem at the same time if I need to negotiate stairs on a ferry, an aisle on a train or any other awkward situation where I lack six arms. It also provide security for the gear as one unit while waiting for transport rather than multiple pieces that can be stolen or forgotten in the rush to board.