Brand new, never been used - Topeak MTS (strap mounted) TrunkBag EX.
Lightweight and spacious - made with flexible 600 denier fabric and rigid molded panels so it will keep its shape. The main interior compartment has an adjustable divider (you can remove the divider entirely if needed). There are also two mesh side compartments that close with zippers and reflective strips on either side.
Bungee cord and mesh pocket on top, storage pocket inside. Removable shoulder/carrying strap, easy access with 3-sided zipper. Tab at back to mount rear light.
This bag has a Dupont Teflon coating for water resistance, but there is an optional rain cover available.
Paid $65 + tax, will sell for $50 (firm)