The number of trips strikes me as plausible. In the case of big cities and their suburbs, there could easily be 5 or more food stores that are regularly visited (Whole Foods, Trader Joes, cut rate 1, cut rate 2, local mainstream 1, local mainstream 2). Sure, some trips could hit more than one of those, but many trips would visit a single store. Between frozen foods, shopping fatigue, and total duration of the trip, people would most often visit 1-2 stores per trip. And this doesn’t count places like alcoholic beverages and other specialty stores (butcher, bakery, etc.).