Some ideas could be:
Fridge Frittata The ultimate fridge-clearer. Any vegetables going soft, leftover cooked potato, cheese rinds, cured meat scraps — everything goes into an oven-safe pan with beaten eggs. You can also try as this as Easy Egg Muffins.
Fried rice Day-old rice any protein, any veg, soy sauce and an egg. One of the most forgiving dishes in existence.
Soup Almost any combination of vegetables, a stock cube, and water becomes a decent soup. Blend in a tin of lentils or beans for protein and it becomes a more balanced meal. Take a look at our Sweet potato & cumin soup for inspiration and technique!
Quesadillas or flatbread wraps Leftover meat, any cheese, roasted veg, beans — fold into a tortilla and pan fry. Works with almost any combination and takes under ten minutes.
Shakshouka Tinned tomatoes, any soft vegetables, eggs poached in the sauce. Bread that's going stale is perfect for mopping it up.
Living sustainably is not about nailing it every time, it is better to have lots of us doing sustainable practices imperfectly than less of us doing it perfectly.
If you want to delve deeper into Food Waste in the UK, you can find it here at STOP FOOD WASTE DAY.