I spend under £400 a month for 7 of us (4 adults, 4 teens, 1 pre-teen). 3 meals a day for 4 of us, 2 meals a day for 3 - they are responsible for their own stuff while at uni etc. That includes all toiletries, cleaning stuff, approximately a gallon of Lynx body spray and all that kind of thing, also all veg for guinea pigs. Other pet stuff comes from Pets at home and costs about £20 or so a month.
I shop in online at Asda and Approved Foods for biscuits, crisps and the like. I don't do top up shops as such, just buy milk and bread 2 or 3 times a week, probably comes to about a tenner a week. This month Asda is about £200, AF about £50 and then perhaps another £75 throughout the month for bread, milk, extra veg.
We eat well and healthily but simply. We also eat mainly vegetarian food with any meat mainly being used as a flavouring rather than a main event and fish being mainly tinned. Fruit tends to be basic sorts like apples, bananas, kiwis and soft citrus, when it runs out, I usually have tinned fruit that we can use.
Typical meals would be HM soup, pasta with chick peas, veg curry, lentil chilli, bulghur wheat pilaf, scrambled egg rice, pasta bake, pasta with cheesy leeks, baked spinach rice, dahl and rice, creamy tuna and pea with rice, sweet potato quesadillas, different bean dishes, salmon loaf, nut roast ....
Tonight we're having a savoury bread pudding (cheese and corn) with green beans and carrots. I have a large repertoire of meals that I can make for between 50p and 75p a head and some that cost less. Breakfasts are cereal, toast, porridge or something like hm banana bread/pancakes. Lunches are leftovers, sandwiches, wraps or simple rice or pasta dishes. We don't really do desserts. There is usually a biscuit or a piece of hm cake for after dinner, occasionally some ice-cream or a homemade pudding. Snacks are fruit, toast, biscuits. I only buy biscuits, crisps etc. once a month and when they are gone, they're gone. I also only buy fizzy water, fruit juice and squash - no coke etc except for birthdays and the like.
If I had more money to spend then I probably would spend more, but not much because, we don't really need any more than we already have. I'm not suggesting that anyone does the same as I do, but if you really want to get shopping bills down, you have to look very carefully at what you spend, eat and throw away and then think hard about what you are prepared to compromise on or do without. A lot of it is about expectations and altering them to suit the circumstances that you find yourself in.