As it happens, I have just meal-planned, listed and then shopped for 2 weeks'-worth of food for 4 (2 adults, 2 older teens / near adults). I need to self-isolate (asthmatic teacher, protecting myself after closing the school last Friday) and wanted to have everything in.
The first week uses mainly fresh food.
The second week uses mainly tinned / frozen food, and long-lasting fruit / veg such as apples / squash. I am also batch cooking fresh food such as peppers etc into home-made sauces and soups to freeze for week 2 (by which time the freezer will be a bit emptier).
There is no food that isn't meal-planned and on the list. The list includes a couple of batches of baking (flapjacks) to cover elevenses. Nobody will be able to snack (except if planned) or - beyond e.g. sandwich fillings - be able to have a choice about what they eat, but tbh that's always been normal in this household.
Lunches - we usually eat sandwiches / rolls and soup, followed by fruit - are the main issue. I have unearthed some couscous / bulgar wheat for salads, and do have 1 small bag of bread flour from Before the Flood. Milk for breakfast cereal and coffee is my best guess at what we will miss most.
It's possible, if hard. I had to plan a restricted menu, as much of what we would normally purchase wasn't available, but i had a long list of possible substitutes (lentils vs meat mince, for example) so bought those rather than leave it for another day.