When I only had £50 a week to shop for all 7 of us, there were a few tricks that I used to keep the food bill down, so that I could still buy drynites, toilet roll and stuff.
We ate a lot of dried beans and lentils in various guises because combined with brown rice, pasta or bread they provide all the protein that you need.
2ce a week I would cook 2lbs of dried beans in plenty water with a couple of chopped onions, some garlic, mixed herbs for white beans and black pepper for dark beans. you can add a few rashers of bacon or a slice of belly pork to the cooking if you like, WHen the beans are cooked you can eat then first of all as is with rice, then you can make them into all sorts of things; mediterranean beans, bean chilli, bean burgers, baked beans, pasta and beans, refried beans, hoppin john, bean and ham soup, garden rice and beans, carribean beans and rice....
ANother thing would be 1lb of green lentils mixed with 1lb brown rice, an onion, garlic, 10 or 11 cups of veg or beef stock and simmer until all the water is absorbed and rice and lentils are cooked. You can eat this as is with salad and grated cheese, or you can season it different ways and use to fill tacos/wraps etc. If you use beef stock, you can use it in place of mince in things. You can also make it into burgers, lentil loaf, veggie meatball things.
Other things that you can do:
last week I had a reduced leg of lamb (2.5kg for £5.50), so I used it for the basis of 5 meals: roast lamb, lamb and barley mince with baked potatoes and frozen mixed veg, lamb rissoles made with 8oz left over lamb, 1lb mash, 1lb cooked mashed veg, a handfull of breadcrumbs, some parsley, salt and pepper and a couple of spoonfuls of the stock I had made with the bone, the shaped croquettes get rolled in porridge and baked, kids had them with beans; meatloaf in sandwiches with lettuce and rootveg coleslaw made from a parsnip, a bit of swede and a beetroot and potato and leek soup using the bone stock.
This week 4lbs of mince have fed everyone but me (veggie) all week. 1lb made meatballs for sub rolls, the rest got cooked with onions, carrots, turnip, a bit of leek, 3 potatoes and 1 1 /2pints beef stock thickened with flour. SAvoury mince jackets, mince puff with parsley potatoes and veg, cottage pie, carrots and cabbage, mince rolypoly with beans, fritters tonight with wedges and whatever veg is left. I bought the mince on the 2 for £6 pounds thing in Asda, so it worked out really cheaply, less than £15 for all the dinners. The mince freezes if you don't want to eat mince every night, so you could save some for the next week if you wanted to.
Other good things to make are soup with bread and some yoghurt or a fruit crumble and custard. You can make a crumble with reduced fruit, if you can get it, or even tinned fruit if you have some in the house. My kids quite like peach crumble or rhubarb and pineapple crumble made from tinned fruit. Cheapest thing is split pea soup, my family like curried split pea soup with onions, carrots and potatoes chopped up in it. Also the ubiquitous pasta with tomatoes, onion and herbs or tomato and cheese rice, patatas bravas with a tiny it of sliced chorizo for flavouring.
Or you could make fishy things from tinned fish. A small tin of sardines mixed with 1/2pint of savoury white sauce, a fried onion, some dried herbs and seasoning can be used to fill a pie, if you make a batch of shortcrust pastry. A 200gm tin of tuna mixed with some white sauce, an onion, salt and pepper and some frozen peas is really nice either in jacket potatoes or over rice. Mix a tin of tuna with a tin of mushroom soup, some peas or corn and a cooked onion and serve over toast or mash. Slice a 1lb wholemeal loaf into 4 or 5 lengthways, mash a tin of pilchards in tomato sauce and spread over the bread, shape back into a loaf and put in a baking tin the pour over 1 pint of savoury white sauce, bake at 180 for about 1/2hour. Make kedgeree using 1/2lb smoked mackerel (you can add 1 egg for every 2 people if you like to boost the protein.)
Remember to plan for leftovers, extra rice can be made into eggy rice for lunches or rice salad, or heated with milk, sugar and cinnamon for a breakfast cereal. Extra mash can be made into potato cakes or scones for a snack or mixed into with left over veg and an egg for bubble and squeak, or even mixed with a little cheese and pickle and used to put on toast. Leftover pasta mixed with tinned corn, a little cheese and mayo is a good, easy lunch for little kids.
Another cheap, easy dish is to cook about 300gms of noodles in chicken stock and some thai curry paste or curry powder, add a cheap packet of stirfry veg and a couple of sachets of creamed coconut or a tin of coconut milk and heat through. You can add some leftover meat if you have any to this. Its popular with the children.
For snacks and things you could get the kids to help make plain muffins or little cookies. It entertains them for free and gives you something to put in the biscuit tin! Scones are really easy and cheap as well.
Sorry, I didn't realise how long this is and how much info there is. I hope that I haven't confused the issue for you.
I think, if I were you, I would plan to divide my meals between beans, mince and tinned fish and spread them over a couple of weeks.
1st week: 2lbs pinto beans made into beans and rice, refried bean quessadillas and baked beans with jacket potatoes
sardine pie and creamy mushroom tuna toasts
mince made into mince roly poly and cottage pie.
Make soup for lunch, cook extra rice to have eggy rice for lunch and rice cereal for breakfast, make extra mash for potato cakes and beans or eggs for lunch and for making potato cheese on toast.
2nd week; 2lbs chick peas, chick pea curry, hummus and pittas, chick pea salad rolls with fires. If there are any chick peas left, you can make a chick pea, chorizo and potato soup with a tin of tomatoes, an onion and a little garlic.
patatas bravas with some more of the chorizo
creamy tuna jacket potatoes
mince pie made with some of last weeks mince and puff pastry
tomato and cheese rice with toast
Soup and bread, pasta salad, curry noodles for lunches.
Hope this helps at all.