A chicken leg and sweet corn nuggets, the first two items pictured in the window menu, are inexpensive fried fare at Chinese restaurants like this in many poorer, demographically mixed neighborhoods. The other items, though not ready to eat, are evidently available for takeout, too: raw shrimp, salad oil, tomato ketchup, and vinegar, all but the last in bulk quantities.
A mini-grocery on restaurant premises is not unusual, though typically these serve, at least in part, to showcase the quality of suppliers and their provisions or the caliber of industry friends and colleagues. Here the rationale is more elemental: to tap into an additional revenue stream, probably a narrow one, by channeling wholesale savings to restaurant customers and passersby alike.
"We can get it for you wholesale"