We use Lidl/Aldi/Netto for for half price fruit and veg, breakfast cereal (we get aldi's version of shredded wheat and no sugar/salt muesli), porridge, wholemeal pasta, tinned beans, chickpeas etc, olive oil (we decant it into a spray bottle so you use less), fresh herbs, tuna, tinned tomatoes, noodles, free range eggs, cheese, milk, plain yogurt, frozen fish, free range chicken, dishwasher powder, washing up liquid, washing powder. Then we go to Asda for unrefined sugar, wholemeal flour, brown rice, salt free pasatta, free range butter, free range butter, bread (you could make your own if you wanted to be really good and were able to get a cheap second hand bread maker or you might even get one on freecycle), spices, bouillon powder, breakfast cereal if we've been to Lidl rather than Aldi as they don't do shredded wheat or no sugar/salt muesli and other stuff you can't get in Lidl/Aldi/Netto.
I also cook big batches of food from scratch and freeze them into portions because it works out much cheaper than buying frozen ready made stuff from the supermarket, is much yummier and if you find yourself caught short one week you've always got back up meals ready to eat.
Do you have a market near you with a butchers? They usually do really good deals and you can ask advice on the cheaper cuts of meat and how to cook them.
Also 60-80% of what you eat should be fruit and vegetables. Only 20-40% should be meat/fish and potatoes/rice/pasta/bread. A lot of people get it the wrong way around and end up spending a fortune on meat.