I can't imagine not having three days food in. I shop once a week, on a Saturday, so Sunday, Monday, Tuesday and Wednesday I always have at least 3 days of food in.
I also keep........
Frozen fish
dried pasta, lentils, rice, couscous
Tinned beans, fruit, fish
Bottled fruit, pickles
Waxed cheese
UHT milk
Wholemeal bread flour and dried yeast.
...so generally have a week's worth of store cupboard ingredients that we could eat if necessary. I have a log burner that I can cook on, and a year's fuel.
It wouldn't be Michelin starred but we wouldn't starve.