After looking for MINI specific trash bags, I turned to an old standby: Trash Stash. Available from many sources, the cheapest seems to be Cargogear at www.cargogear.com, $12.00, but I didn't compare shipping costs. Hangs from the headrest (of the passenger seat) and easily accessible by the driver. Leakproof, too. Had one in my old Landcruiser and it worked well.