Anything you can bulk out with beans. For example, I make Spag bol for 2 with extra lean beef mince, then with the leftovers I add a tin of kidney beans, some spices and a tin of baked beans and make 2 more meals of chilli. Yummy!!! And rice is cheap to go with it.
Soup is very cheap, and you can make it from whatever veg is on offer when you are shopping.
As has been said, SW chips. I believe that mug shots and pasta n sauce are cheap too, although I can't eat them as the flavour enhancer used in them gives me migraines.
Stirfry veg and noodles, cheap and quick and easy.
Look out for reduced/on offer meat. For example at morrisons at the moment they have 400g of chicken (approx 3 big breasts in a pack) at BOGOF £4... I bought 6 packs, opened them and split them into bags with 2 breasts in each (for 2 people) and have stuck them in the freezer. I used to do the same at uni.
If you can get bacon on offer, that's always a great standby, as are jacket potatoes.
You can make very cheap tomato sauce for pasta with a tin of tomatoes (about 34p) some worcester sauce (storecupboard essential in my book!) dried herbs, salt and pepper, onion and garlic, with a tbsp of tomato puree if you want to for 1/2 a syn. This costs about 50-60p and makes enough for 2 meals added to veg and/or meat. Bargain!
Hmmm... hope that helps... I was at uni for 4 years and have been unemployed for a while, so am not bad at budget meals and stretching things wherever possible.
A major thing is to shop around if you have the time. I have been to asda, tesco, morrisons and waitrose this week, and will go to aldi and/or lidl tomorrow for some fruit and veg. Will check out offers first online and see which I fancy!