Pretty much anything goes into Use-Up Stew or Use-Up Pie. It's generally fine, often even very nice.
Contemplating this week's leftovers, I've got a portion-and-a-bit of fish stew (lots of green veg, herbs, mushrooms, potatoes), and a portion-and-a-bit of Spag Bol (more accurately Rice Bol), as well as the usual odds 'n' ends of veg.
If I put them together, would it be edible, I wonder?