In a grocery line, I put a checkout divider after my items. It’s the thing to do, the kind of social glue that makes for a nice day. And if I have thirty items and the one behind me has two, it doesn’t make me any smaller by letting the person go ahead of me. When using a basket, of course you stack it on the floor after emptying. And I have never pictured it to be a store clerk responsibility. The same mostly for security screening, so I’m with OP.