re: OT food industry people- Where does all the leftover food go?

At pizza hut, the food that passed the expiration date was more or less taken back into the cooler and relabeled and used. Pizza's that someone didn't come pick up was normally just taken home by a worker or thrown into the trash

Mcdonald's we would count up the unused inventory(patties that past their hot plate shelf life, dropped patties, wrong orders, etc) at the end of the shift and then throw it away.

Same way with the sunday leftovers at this restaurant i worked at in high school(they only had a lunch buffet on sunday mornings, every other day was normal operations), and leftovers were either taken home by employees or thrown in the trash