I like the idea of calling it "planned overs," especially since my family doesn't like the idea of leftovers. On my meal plan, I have a day listed as "Dragon." When my husband asked about it, I said, "whatever we drag-in from the fridge or freezer."
I've messed up my fair share of soups, broths, and breads by adding a "bit of this leftover and that scrap." My defense is I didn't grow up cooking, much less scrap cooking, so I'm learning and developing that intuition of what pairs well together and how much to use. Sometimes the disasters have negated the financial savings, but I always learn something for next time.
I've been experimenting with my favorite banana bread recipe. Herbal cherry was one of my favorite versions, using up some cherries and herbal syrup that I had in the freezer. Pear parsnip was a really good one, too, as was chai fig.
For savory muffins, I use odds and ends in this
Tex-Mex muffin from Weelicious. I've omitted or changed out the veggies and chicken, left out the cheese, used broth or sourdough starter in place of milk, and used leftover salsa or diced tomatoes instead of tomato paste.