The key is shopping around.
I do a monthly Iceland order for chips/burgers/cocktail sausages/popcorn chicken/chicken fillets. Frozen veg. And my wash powder is massive from there and only £10 (last 2-3 months) the sausages and chicken are good for lunches.
Weekly Lidl - spent around £40-50. Make a list and stick to it.
Monthly savers shop for all toiletries, damp boxes, fabric conditioner, surcare, stain remover.
I make sure I plan crappy easy dinners for when we are busy or on Fridays when I'm tired. I always have pasta 30p and jar of pesto £1 in cupboard. Plus hot dogs, tin spaghetti, beans, frozen veg. So I can throw meals together.
I buy reduced meat when it's silly prices then freeze (whole chicken for £1, packs of sausages/mince for 50p) dh works in a shop and brings home bread/meat that's getting chucked we always have a loaf in the freezer.
I order a sack of 25kg potatoes from the greengrocer for £10 which is cheaper than supermarkets, taste better and I always have a meal in!