Spanish Omelette is a good one - Sliced potatoes, onions, peppers if you have any, eggs, dash of milk, salt and pepper. If we're having a meal using baby potatoes i will cook extra and slice up to make this the following night or a couple of tins of value potatoes (around 19p) are cheap and easy.
Slice the potatoes and fry them along with the onions and peppers (if using) until veg is soft and potatoes are golden. Add your egg & milk mixure and cook on the hob until the egg is setting , then sprinkle with grated cheese and finish off under the grill. Serve with salad or baked beans. I make a huge one using 8-10 eggs and it feeds 5 of us plus leftovers are taken in lunchboxes the next day.
Stew is cheap and filling - onions, potatoes, carrot, swede/turnip, a handful of pearl barley and whatever meat you fancy. I usually use leftover roast chicken plus the chicken stock. Serve with dumplings on the first night then the next day add a pastry top to leftover stew and serve with chips and peas.
Soup 'n' pudding nights are a favourite in our house - a big pan of hm soup and crusty bread followed by a hot pudding with custard. Favourite soups are potato & leek, pea and ham or carrot & coriander and puddings are either a crumble (apple & blackberry atm) or a suet sponge pudding, either jam or syrup.
hth