I've seen this three day supply of food mentioned in several articles and have wondered about the source.
Anyone who has paid attention to to the news in times of natural disasters and/or civil unrest has watched video footage and has seen mobs strip these stores clean in a matter of an hour or two, leaving empty shells of buildings with broken glass and broken doors. A full out power outage and these stores are out for the duration. Doubtful that they would ever be restored even after a power recovery as the demographics of the areas served would have been drastically altered.
Having lived in Manhattan for several decades I can attest to the general paucity of suburban type supermarkets. Small mom and pop grocery stores are the rule. But the real weak point is that most urbanites rely on local restaurants and take out places for most of their meals. With non-functioning cold boxes they're out of action in 24 hours.
Baby, it’s cold outside,,,
Urban "groceries" of all stripes would be stripped of food in a matter of hours.