Making meals cheaper (and better) -
My lasagna/bolognaise sauce is full of veg because I do big batches and it doesn't feel like faff to wash out the mini food processor when I need to dice 3/4 onions, so I also whizz up a few carrots, a large handful of mushrooms, a red pepper, perhaps half a courgette etc to add to the sauce. Family half know I do it, but ignore that it's chock full of veg they don't normally eat (I don't usually admit to the courgette as DD won't eat it - but loves it when she doesn't know).
Shepherd's pie meat mix also has a load of whizzed up veg, but I also add whole peas.
Chilli also has a load of veg in it in chunks - tomatoes, peppers, kidney beans etc - and we do a veggie version as well.
Veggie curries with a tin of chickpeas along with the other veg are great also.
Bulking out dishes with veg is often a lot cheaper than loads of meat.
I buy the own brand easicook rice and pasta normally - not the absolute basics version (SV basics pasta is 49c for 500g, but their own brand pasta is 99c for 1kg - a difference of 1c if buying 1kg in total).
I tend to buy a lot of cheese and we like stronger mature cheddar - but Kilmeadan often has offers of the small block for €2 including the mature and extra mature, so I stock up with the offer as it lasts weeks/months in the fridge.
M&S do packs of individually wrapped chicken breasts, which are really handy for the freezer. But I also buy trays of freerange chicken breasts and boned thighs, and chop/freeze them myself.
Lidl's double packs of bacon lardons are great! They last ages as well in the fridge, and 1 pack is enough to fry and add to lots of fried mushrooms and an onion, dash of cream and some grated parmesan - or a jar of tomato sauce (or HM tom sauce), for a dinner with pasta. Or to add (already cooked) to other veg and leftover chunks of potato with eggs for a substantial Spanish omelette.
The various 49c veg offers usually have at least 1 useful thing in them. I always have carrots and mushrooms and a couple of peppers in the fridge. If I have summery veg (peppers, courgette, mushrooms, onion, garlic etc) that are starting to need to be used, I will dice them together and roast them, and freeze them to use in a plain tomato sauce, maybe with some bacon bits, chopped up sausages or some chicken or prawns from the freezer with some pasta.
I also have things like curry pastes and other marinades to put over meat when I take it out to defrost (night before or early morning), and give lots of flavour to cook later.
And I freeze bits of things leftover - so if there are a few small slices of pork left from a roast, I will use those along with some prawns and a bit of chicken and lots of veg for a Chinese stirfry. Or a half portion of a sauce from dinner might be enough for a lunch at work another day or a snack when someone comes in starving to keep them going until dinner. It's not always just about freezing a whole dinner-sized portion. I have also found that freezing dinner-sized amounts in single person portions have been useful for allowing us to juggle nights when there are only 1 or 2 at home rather than all 3, or to have different things (a chicken, a lamb and a veggie curry - maybe all on the table like a takeaway, or maybe each person wants a different one - but everyone having rice).