I’ve never really had that problem, because I almost always carry a large-ish backpack with a cotton bag folded inside, but it would be neat if stores had a box near the checkout where you could leave your extra bags for other clients to use for free.

One of the libraries I go to does something like that, they keep some bags near the front desk and give them to users who need something to carry their books. I’ve given them two bags I had no use for. And I know a bulk food store where you can leave empty containers for other clients to use.