We do about £60-70 and thats for 4 not the cheapest here by far. One shop a month will be higher as this is the stocking up week. Its all old fashioned ways really, we have a well stocked store cupboard the kitchen cupboards and a space in the utility room which is currently just a big plastic box of cans and rice and such (like Nigella's pantry but the aldi version) and the freezer is so well organised it makes the former rebel in me sob. Sorry if i repeat what others have said.
Shopping around too for offers online and in shops, currently have vouchers for sainsburys where if you spend £60 you get £12 off tesco currently has a spend £40 get £5 off next forty pound shop.
Ingredients this is my best tip, cooking from simple ingredients, rice, pasta, lentils, couscous, baking cakes and biscuits, making soup, freezing half, making left over stew into soup, curries.
Phasing out crisps...
fizzy mineral water supermarkets own brand in a little pure juice is half pop half juice and lovely.
I've found medium sliced bread lasts longer, we only need two loaves a week now, I bake bread as well but am not good enough to get it right for sandwiches.
proper planning see what you have in, what can go with it, after a while you'll know what your staple foods are what you rely on. A proper meal planner and list.
We all use same soap, baby soap, baby shampoo and I borrow the matey bath!
I don't make separate kids meals
A basic cake and a basic pastry recipe are live savers
some of my always have in staples are parmesan (its expensive but goes a long way and is as useful as salt) a mixed bag of chillies, flour, eggs, butter, honey, porridge, mixed fruit, pasta, rice, risotto rice, garlic, onions.
cheap basics chocolate to tart up home baking. (I'm making rocky road later)
i'm such a bitch, undercoverprincess there was a time my oldest wouldn't eat things like stew and cottage pie, but he just had to learn to, youngest has been raised on a budget (her mummy and daddy grew up a little) :) there are loads of cheap ways round food, it doesn't all have to be like old school dinners.
If you can't bare cooking go the way of the basics ranges, but we would have to spend so much on feeling full if we bought ready made things, we eat less now but its filling. So maybe if one night we do have hotdogs (and we do) only a bit later we are all starving! so its tricky not to have to spend again on a snack. If you are blessed with small appetites this isn't so important. :) DH makes homemade popcorn, so cheap. Kids love it.
Filling up at meals saves so much money. For us. You'll find a way for you, everyones different.
(the basics blue cheese in sainsburys is very very very nice I'm making potato cakes with it later, and this on my eldests birthday.. so flash here, but we are going to the theatre afterwards)