Pizza box that converts into serving plates and storage container.
The "plates" aren't that clever, but I do like how the box folds in half to store leftover pieces. Yes, I know the frying pan trick to reheat a slice of pizza (the trick is: use a frying pan to reheat a slice of pizza). This works quite well in a Frank S-style nonstick cast iron skillet.
If you usually pick up your pizzas, as opposed to having them delivered, I can also recommend an insulated pizza delivery bag. Despite decades of indoctrination that characterized pizza delivery bags as professional-only tools, civilians are actually allowed to own them. Amazon has plenty, and the single size one costs about as much as one pizza.