There are plastic food containers designed for pizza slices that will fit in a RV fridge. I bet your local pizza shop would sell a box in the size that would fit in the fridge to keep the leftover pizza in.
We use ziplock bags too but no longer will let dad help. To save money he likes to cut off the point piece of the slices so that it would fit into a sandwich baggie. Nothing like finding butchered pizza slices along with a bag of "pizza points".
Great choice for "Living within my means" and camping for one...
2011 Salem Cruise Lite 20RBXL & 2011 Toyota Tundra Dbl Cab
Camping History: 45 Trips / 133 Nights / 3736 Miles
FRF Social Group: Campers of the West