The Hase Kettwiesel Luggage Bag, made by Ortlieb, has a very large main compartment, large enough to fit two full grocery bags with room to spare. This bag is huge! There is one inside pocket and two outside zippered mesh pockets, and it mounts by attaching to the back of your Kettwiesel seat using pannier style clips. Made with a mix of PVC-coated polyester and Cordura, this bag includes reflective stripes for better visibility!
