It’s a really good question.
The rich are escaping on private planes to tropical islands or their own bit of desert. Well off preppers appear to have spent hundreds, if not thousands, on filling their barns and garages with water purification tablets, medicines and loo roll. And everyone else has to read about all this while knowing that even a slight deviation from the weekly budget means hours on the phone pleading with landlords and fuel providers, and endless explanations to disappointed children ...
As everyone else has said, OP, start with what you’ll need if you’re too ill to get to a shop. Breakfast - tea, coffee, milk to store in the freezer. Bread takes up room, but if there’s a baker in the house then extra flour has a million uses. Plus oil/butter. Sugar. Oats. You’ll want fruit - either storable, like apples, or frozen.
I’d stock up on beans and pulses for soups and casseroles that can be made in advance and frozen.
Do you have a garden or anywhere to grow stuff? Invest in seeds. Growing some vegetables and herbs will provide entertainment if you’re all stuck at home - and you’ll be glad of the produce to add variety, eventually.