I only get one food delivery a week so often rely on frozen or dried veg and fruit by the end of the week, plus cheese and ham omelettes.
I bought some dried berries, plus dried broccoli, cauliflower and leeks - the dried and frozen berries are good in yogurt and dried cauliflower with leek/broccoli makes a good cauliflower cheese if you reconstitute the veg in milk & water. I have frozen rhubarb to make a ground almond topped 'crumble' when it is out of season.
I bought the dried berries and veg from a couple of ebay shops, and from buywholefoodsonline.
I can't eat much butternut squash, too high carb for me, but frozen cauliflower rice is good or fresh courgettes keep well. (I have a cheap hand spiralizer for prepping courgettes.)
I always have extra eggs and cheese in the fridge and some chicken portions and fish in the freezer, but you could store tofu for protein? And frozen avocado is good for making guacamole, etc.
I also found an online shop that sells dried whole eggs - not a great substitute in scrambled egg or omelettes but a tablespoon makes up a good low carb mug cake.
I keep a few tins of coconut milk and tomatoes in stock. I also have some cartons of UHT cream (one that does not have sugar or thickeners in).
All this plus ground almonds and coconut flour for making low carb bread and cake means if the online order fails, as it did the first 3 weeks of lockdown, I have enough stock to make low carb meals.