Running a store is one of the most common informal economic activities inside any correctional facility, and it works exactly the way it sounds.
An inmate with consistent commissary funds or strong outside support uses their purchasing power to build up an inventory of high-demand items from the commissary. Things like ramen packets, chips, coffee, candy, hygiene items, stamps, and whatever else moves quickly on the unit. They hold that inventory and sell it to other inmates between commissary days or to people who have been placed on commissary restriction and cannot shop for themselves.
The catch is the markup. Prison store economics do not run on cash. The currency is the items themselves, and the going rate is typically two for one. You borrow one ramen packet today, you pay back two ramen packets on your next commissary day. That is a 100 percent return on the original item, which is why running a store can be very profitable inside.
For the inmates buying from the store, it fills a real gap. Commissary visits happen on a schedule, often once a week or less, and hunger and cravings do not follow a schedule. Being able to get something between commissary days at a premium is still better than having nothing.
For the person running the store, the risk is proportional to the operation. A small informal store between a few cellmates is low key. A larger operation that spans multiple housing units draws attention from staff and from other inmates who might want a piece of the business or want to eliminate the competition. Your boyfriend's roommate is navigating that risk calculation every day.
It is worth knowing because anything that happens in that cell involves your boyfriend whether he is running anything or not.