It's a very tight budget OP.
We are a family of four, 2 adults and 2 DS I had to change my ways since I stopped working, currently on maternity leave. My OH is self employed so very uneven income.This is what I do.
Every week I menu plan. I first look in my food cupboard to see what I can use and then I write a shopping list based on my menu plan. It sounds time consuming but it takes me literally 5 min.
I have got a standard shopping list on my phone, things that I buy/need everyweek/don't want to run out ( toilett paper, tea, coffee, sugar, milk, bread, cheese, yogurth, porridge, pasta, rice, oil, seasonal fruit, washing up liquid etc) so a quick look around to see what we are missing is all I need before I go shopping.
Also got a writing pad in the kitchen in which i/ we note down things that are getting low/ finish as week goes by.
I do my main shopping at Lidls, I am very careful when I go in to a shop for a top up, as I can get carried away and spend 20 pounds just when I was popping in for milk.
I try to avoid the shops so I don't get tempted
I always pay cash, don't carry my cards unless absolutely necessary
I cook mainly from scratch
For breakfast we have porridge or toast and for special occasions/ weknds crampets or pancakes
For lunch i make vegetable soups, baked potatoes, beans on toast, left overs from the day before, omelette, smthg easy.
For dinners, I cook lots of casserole dishes, curries, chillies, pasta bake, vegetable bake with creamed cheese, sausage and mash, fajitas, pasta bologna, lasagna, etc
I cook in whenever I can so for instance if I buy a kilo of mince I would bulk it up with lots( and lots) of veggies and tomato and I make pasta bolognesa, lasagna and chilli. Freeze some.I don't want to be cooking every day!
I looooove my slow cooker, I use it all the time.
We don't have fizzy drinks (can't afford them) just water or squash
We don't have desserts every night.
I kind of take budgeting for food as a challenge and a way to use my creativity, makes me look quite boring, I know, but I hope I was helpful 
Good luck OP