The closest grocery store to me is a small Mexican place called Azteca. It's a tiny place, maybe six aisles, in a tiny building. And in addition to the produce, the dry goods, the meat, the dairy, a bakery, all the things you'd expect from a grocery store, it has two restaurants, a check-cashing place, a clothing store, a little desert shop, a cell phone kiosk, and a key-maker.
A few years ago, the local Safeway became an Avanza. Now it's a Mercado. When it was a Safeway, it was a grocery store that had a bank and a pharmacy. The bank and pharmacy are gone.
The cart corral has been turned into a hair salon. The niche where the vending machines sat is now a key-maker booth. Back where the pharmacy used to be, that's now separated into a clothing shop on one side and a CD shop on the other. The bank? It's a jewelry store now. Oh, and they have a little kiosk where they sell Mexican sodas and those little orange wheels.
Now I'm not up on all the details and the business arrangements, but I'm pretty sure that all of these little shops and vendors are NOT run by the Azteca and Mercado companies. Azteca and Mercado rent the space out, of course, but these booths and kiosks are operated by the owners.
I doubt there's much money to be made selling duplicate keys or duritos, but at least they're making their own way, and more importantly, have an institution (the store) that gives them the space to do it.
When I was talking the train, I often wondered why RTD didn't engineer space for vendors at every station. I mean, why not? Leasing out space to a vendor would help pay the overhead. The streams of people every fifteen minutes would provide the vendor with lots of selling opportunities. Thirsty riders would definitely buy a cup of coffee or a newspaper. So why not do it this way?
I have no idea. I'd be curious to see if the idea was even considered.