Campbells tomato soup can be stretched quite far by adding a chopped and gently fried onion (and garlic if have it), a tin of tomatoes (I buy whole and chop to desired size), italian herbs (dried oregano and basil, pepper) and the usual tin of liquid (half milk, half water is our usual to make it creamier - in fact, whole tin milk and half of water again works well to stretch even further as creaminess disguises stertching).
Campbells mushroom, chicken, chick in white wine - any of those can be mixed with chicken (diced and fried) and mushrooms to serve with rice or mash. Dash of cream or milk (or chick stock or white wine) to loosen a little. Some tarragon or parsley if you have it gives it depth.
Tin tuna, half tin sweetcorn, loads of old veg from fridge (including an onion and garlic) and leftover cooked rice (and frozen prawns maybe) fried up with some mild curry powder makes a nice dish mostly from stores. (I use both tuna in brine and oil for different things - but tend to use oil one for this as the oil goes into pan for the cooking, extra pennies saved and extra flavour gained).
Pasta with garlic fried gently in a good slug of olive oil, with a handful of frozen prawns thrown over the top, all mixed together, is nice (squeeze lemon juice brings it all together!).
I try to have a tin of bamboo shoots, tin of beansprouts etc in the cupboard to make a stirfry.
Always have onions and garlic.
Lidl's double pack of bacon lardons, and their chorizo sausage, have long fridge life and many many uses.
Frozen cooked prawns are faster to defrost (throw straight into sauce) for an emergency dinner - heat a jar of tomato or curry or chinese sauce with prawns, and veg if have any, while rice/pasta cooks.
I always have dried mushrooms and usually risotto rice - I make a few different risottos, but mushroom one from dried mushrooms is handy for "just before big shop" days.
Usually have chick or veg stock in freezer, but stock cubes for emergencies too.
My cupboards are a very varied smorgasbord, I can rustle up a big variety of meals and treats in minutes usually - but I do have to remember to empty them out at the back at times....