If serving dishes were used instead of just presenting somone with a plateful, then it is hygenically acceptable to reuse any food left in those dishes at the end of a meal. eg - cold mashed potatoes can go into homemade fish cakes, cooked veg can go into soups and omelettes etc. Reheating meat is not recommended more than once and then it needs reheating very thoroughly.
Wasting food is just not the way I was raised - during post war rationing.
There was no junk food then, which is probably why it gets left in the 1st place -I cant think of any way of reusing cooked potnoodle, but I never eat it so havent tried
