Pack this… a re-usable tote bag

Bring a re-usable bag. A grocery tote I find is best.
It doesn’t have to be big. I like a big one though or two small ones. I also prefer one I can fit over my shoulder. Many cities and stores are adopting minimal charges for plastic shopping sacs. The reusable bags are often more durable than the thin plastic of a grocer’s bag. Thus saving you from having it rip halfway back to your hotel and have to carry your goods in your arms.  It can have alternate uses as an extra carry on for all those fragile purchases from your trip, a cover to sit on in a grassy park for an impromptu picnic.  I get a lot of mileage out of mine. My favourite re-usable totes are from DM in Germany and Marks and Spencer in England.