The supermarkets I go to are too crowded, and too rush-rush-rush, to be able to interact with other shoppers. That's because although they are large chains, the supermarkets themselves occupy small spaces because they're in compact city centre environments. The time of day I'm in them doesn't help, walking home from work at the same time everyone else leaves work. But even if I go to them later in the evening, they're too crowded.
When I lived further out of town, I shopped at a very large supermarket, and that was a lot of fun. It still wasn't conducive to meeting and getting to know other shoppers... I don't know, it's just not a place where you can spend any length of time with them, or as others have said they're not there to meet new people. Yet they still offered me a better bite at the cherry in terms of meeting women, because I was able to get to know staff members, being a regular there. In this less crowded, rushy space there was plenty of opportunity to chat with staff members as they worked on the floor, which passed the time for them and would have helped them get through their jobs because they had interaction.
Flirting and sexual innuendos were not unknown from checkout staff (with whom no genuine interaction was possible because you had like two minutes at the till, and their flirting was of course intended to tempt you back for more sales). Example: a checkout girl serving the people before me handled fish as part of their groceries. Then she served me and the conversation went "Hello... How are you...", then swiftly moving on to "I'm smelling of fish".