Hi Sonnet
Well we have a monthly budget of £150 and that is 1 child 2 adults various visitors for dinner and the dog. It includes alcohol. The other thing we do is have a housekeeping pot of about £50 a month (which NEVER gets used up completely) for the fresh milk, bread, more fruit and veg thru the month when the delivered stuff is used up.
We online shop and have been since about 1999 I think, I find it helps keep the cost down and time.
Concentrate on the essentials, fruit and veg etc and make up your meals yourself do not use ready meals. If you make a big dinner one night, portion control and put some aside in the freezer for another day.
You may need to reeducate that toast, ready break and yoghurts are the breakfast, this is fast food but also healthy food.
My son eats a bowl of cereal or porridge, two small petit filous and a rusk to dip into them for breakfast, at weekends we usually have boiled eggs or poached eggs and now and again bacon rolls.
Watch the meat portions too. I find that mince is now sold in such huge containers that people use the whole thing. Either separate it into two or cook it all and freeze half.
Buy a HUGE bag of spuds, if kept folded at the top you should have enough for a few weeks at least and they should last too.
I know I have waffled on, but this is something I am good at budgeting and watching the bills.
I use my supermarket.com too, it helps you shop around.
Good luck.