I tend to buy one big monthly shop of about £80, then three smaller shops of about £50. On top of this, our milk is delivered and we all have hot dinners at work / school. That said, my children have a second hot meal most nights.
I find what keeps it relatively cheap for us is the fact that I don't eat meat, hubby and children eat meat out of the house, but generally not in it so we only ever buy fish or quorn and that is a lot cheaper. I also naturally buy own brand (but not generally value price) rather than branded food, and don't tend to buy many snacks. I think it also helps that my children are out of the house a lot, so don't graze at home.
Our food tends to go something like this...
Breakfast: own brand cereal or porridge every day.
Lunch: eat out.
After school snack:* cheese, ham and crackers / sandwich + salad (tomatoes, cucumber, celery, carrots etc). I make up pots of this every day for the dc, value crisps (only get these because they do them in 18g packs, and I don't like the Dds eating big packs of crisps). Piece of fruit (whatever is on offer that week, usually there's a pack of nectarines, plums etc for a £1 a punnet), and something sweet (cake bar, yoghurt or cereal bar).
Tea: this varies depends on what my Dds are doing that day, but is usually things like:
Macaroni cheese, steamed fish rice & vegetables, chilli con carne / spag Bol. These will all be made from scratch (but I do use a jar of sauce for spag Bol etc)
Other light teas will be fish fingers & chips, beans on toast, pizza or jacket potatoes.
We don't have puddings during the week, only fruit or yogurts. I don't buy expensive children's yoghurts or cheese strings. Girls tend to drink water, but we do have Squash and lemonade at mealtimes, or milk. I don't buy any lots of kitkat type biscuits, just custard creams and the like. If they want to snack between meals, there's fruit or toast but that's about it.
However, I don't buy this to keep my meals cheap, it's just I'm a pig and would eat all the crap within 15 minutes flat I'm trying to encourage my children to have a healthier relationship with food, whereby they eat their meals and not tons of crap in between.
- the huge after school snack is because my DDs do competitive gymnastics and often have three hour training sessions after school (eldest DD), so she has hot school lunch, big snack after school & before gym and then smaller hot dinner after gym.