I was born and raised there. I've lived in places with a 5 foot kitchen (24" stove, 6" landing, 18" sink, 12" landing) with the only cupboards above this. (That was the kitchen - the "back" was the living room.) I had more than 3 days worth of food in those cupboards. You had to worry about roaches so everything was in jars and the shelves were lined with jars of rice, beans, lentils, pasta, tomato sauce. I would buy 50 pound bags of rice and bags of dried beans and lentils and boxes ramen noodles and pasta. (Those were my starving student days.)
So, even in a small space people have more than 3 days of food.
Re batteries and other supplies (candles, oil lamps) yeah people are woefully unprepared which is why I think the lack of electricity is the real problem. You live above the 10th floor or so and you need electric pumps to bring water up to your floor.