We always called this Mish-Mash cooking.
One of my favourites is pasta with smoked sausage and pepperoni, in with whatever veg I have (usually mushrooms, peppers, courgettes and onions) lightly sauteed and then either pour over tomato sauce or stir in some Philadelphia (the basil one or the garlic and herb one are particularly lovely).
I also dreamt up a recipe of one of my favourite soups this way - I used a tomato base, threw in whatever herbs and spices I fancy (usually basil, oregano and a little touch of chili), add some sauteed onions, a can of chickpeas (drained) and some diced chorizo. Mmmm - delicious!
I often clear out the veg in my fridge making vegetable chilli in my crockpot. I just chuck in whatever veg I have with some kidney beans and a tomato sauce with loads of chilli power and Robert's your mother's brother. Leave it simmering in the crockpot for several hours on medium-high and the flat smells delicious.
I do the same with curry - leftover meat from the Sunday roast (chicken, turkey, beef, whatever) with loads of veg and a curry sauce. Whack it in the crock pot and away you go.
Today I made pumpkin soup to a recipe I discovered by accident - an entire pumpkin, roasted and scooped out into a pan, a leek (finely sliced) some stock (veg, chicken, whatever), nutmeg, cinnamon, clove, salt, pepper and a touch of chilli powder, and then the secret ingredient - a generous dollop of smooth peanut butter to add richness and bite. Simmer then whizz with a hand blender till smooth. I made a HUGE pan of this today and my flat smelled divine. I even froze some for future enjoyment.