Buy what's on offer and in season. That means not buying the children punts of strawberries in January. Frozen fruit and some frozen veg are absolutely fine. Those little punnets of fresh imported fruit can be more than a week old when you get them. Have a serious talk with the others in the family about why they can't always have what they fancy when they fancy it. Let them choose some of the recipes.
Look at what you're throwing out, week after week. We were chucking out avocados that we'd let get over-ripe. Now we don't buy them unless they are part of a meal plan and will definitely be used. Bananas gone over? Make BBC Good Food's banana cake or mush them up and freeze for instant banana ice cream.
Drop meat at least twice a week and have a lentil bolognese and a chickpea curry or a veg tagging or chilli non carne or similar. Learn to do lovely Italian pasta sauces from scratch: mushrooms, onions, cream, parsley and you can have a big bowl of lovely tasty comforting fare for £1 a head. Big stir fries with whatever's in season (buy fresh veg and chop yourself, don't buy things pre-grated and chopped) and a few bits of chicken or whatever over the top. Make your own stir-fry sauces with garlic, ginger, soya sauce and so on. Don't buy little single-use sachets or packets. Buy a whole chicken, roast it for one dinner, use the leftover bits for another meal. Buy a large pack of mince and use it for a lasagne and a shepherd pie.
I always have spring greens in the fridge. 70p for a big bag, just rinse, chop and steam for green goodness that costs far less than broccoli or spinach. Steam, add some soy sauce, butter or lemon and pepper (sometimes all of the above) and serve them on the side. If you like caraway, add some caraway seeds.
Latest discovery, Coronation chickpeas. Can of chickpeas (40-50p), a couple of tablespoons of mayo (Bramwell's (Aldi?) is better than Hellmans and half the price), some finely diced onion, some mango chutney, a tsp or so of curry powder, lemon juice. Enough to fill four pittas or wraps with some salad leaves: ridiculously tasty. £2.50-ish for lunch for four people.