Planning well ahead and buying a little more each time leads to full cupboards and freezers and doesn't prevent anyone else from buying. You do have to use the oldest stuff first, of course.
The detail of my fresh vegetable buying was a 1 kilo bag of mis-shape carrots, a 1 kilo bag of onions, one sweetheart cabbage, and four baking potatoes. I also bought some braising steak and some chicken thighs. In my store-cupboard I already had red and green lentils, tins of haricot and other beans, a shrink-wrap pack of beetroot, a couple of tins of tomatoes, plus stock cubes. These are what I have turned into soup.
I also already had some supplies, bought gradually over previous months as part of my normal shopping bought over previous months,
I have no car, so if the weather is bad or I don't want to walk down the hill and back with a load of groceries, I need to have stores of dry goods and tins. Relying on deliveries from Tesco is all very well, but they have a minimum order level, or they add £4. When I do get an order, (not every month) I make sure it is over that £40 mark by adding long-term staples.