Hey,
I know how hard it is- 5 of us here with DS1 just moved back after uni & he never stops eating (I adore him & delighted he's home, but the food!).
I think these will be standard things, but what I do:
Use my chest freezer well - batch cooking/ reduced meat or bread. e.g. my Aldi always seem to have sourdough 50% off, so I buy loads.
Cook vegetarian for everyone 2/3 times a week (I'm vege so it makes sense).
It's soup season- easy/cheap/filling. I make pastries to go - pre-rolled pastry is £1 in Aldi.
I use my slow cooker a lot- minced chicken & loads of veges makes superb chilli. 500g does my 4 with big appetites as it's packed out with veg.
Frozen veg from Farmfoods is inexpensive & brilliant - onions/garlic/peppers/leeks/asparagus/butternut squash (soup even easier).
Farmfoods if you have one is generally great- good butter is £1, Fage yogurt £2.50, 10 large local eggs £2 & a myriad of brands for chocolate/crisps/store cupboards/ laundry/toiletries. In fact, I rarely buy anything frozen apart from the veg.
Eggs make a great meal.
Frozen fish with the eggs makes great kedgeree- a favourite here.
Laundry stuff at Sainsbury's is really good.
Aldi 24 toilet rolls is 3ply & £4.99
Morrison's do a frozen offer 2X main & 2 X dessert for £10. Their madagascan icecream is in the offer- it's divine & usually £3 a small tub- so I get 2 of those & 2 posh pizzas (normally £6 each) as a Friday treat.
I'm lucky to be near loads of supermarkets, though. And Home Bargains for toiletries!
Other than that, don't buy rubbish you don't need & use Vinted for really decent clothes.