For a treat Sainsbury's do a £12 del of a main, a side, a pudding and a bottle of wine.
OK that's not really saving but I do think everyone deserves a treat occasionally.
Pasta is cheap and if dried lasts for ever, try frying some mushrooms, add some cream cheese and some pasta cooking water. You can also add in bacon or peas or what you have to hand.
I make an Asian broth made with boiling water, a cube of frozen ginger and a cube of frozen garlic.
That's the base, then you can add veg, meat, noodles, chilli, spices.
Use the stems of broccoli and cauliflower as a different veg. They taste the same as the sprouty bits and make a good base for a soup.
Add different things to your baked potatoes, not just cheese and beans but chilli, scoop out some flesh, put an egg in and bake, cream cheese and chives, crème fraiche tinned tuna.
Then repeat with sweet potatoes.
When you are working at home veg soup with bread can be cheap, add in some spaghetti / pasta.
Once a week have 'something on toast', it could be egg, beans, a combination eg beans and bacon, cheese.
Plan to have left overs too. Eg on the day you do baked potatoes cook more potatoes, the next day you mix the potato flesh with flour to make gnocchi.
Start watching Atomic Shrimp' on YouTube he does shopping and cooking challenges and has some good ideas to use things like beef paste in recipes.