This. I was perfectly content with dry leftover pizza the next morning, but my wife started layering the slices with parchment paper in a huge tupperware container. Too legit for me, but it works! Day old pizza rocks!
(Grew up next to a family that would order an extra pizza for supper, that’d go right in the fridge for breakfast)
Once it cools to room temp, and don’t wait too long, freeze the slices in a ziplock bag minimizing the amount of air within. Good for at least a month.
Once ready to eat, pull out of freezer and put in oven set to 375. I generally put the frozen pizza slices on foil and right into the oven, allowing it to thaw in the oven as the oven warms.
A dissenting view is that leftover pizza, frozen or not, should be gently heated for 30-45 minutes in a low 250F oven. I don’t do this because (1) I like a dark and crispy crust (2) Don’t notice that much difference and (3) Am often too impatient to wait 45 minutes.
“Leftover pizza” has to be the world’s greatest oxymoron.
Where pizza is concerned, almost any suggestions that result in ultimately eating the pizza are fine. I have almost no objections to any of the ideas above. EXCEPT: paper towels between slices of pizza. When the cheese congeals with paper towel on top of it, the result could be paper towel glued to the pizza. Yuck. Either don’t separate the stacked pizza slices, or separate them with freezer paper or waxed paper - something that will peel away cleanly without leaving residue on the food.
If you have the time and inclination (and aren’t restricting calories), one great way to eat leftover pizza is by blackening it in a cast iron skillet. Heat the pan, add a little olive or other oil, then slap down a piece or two of leftover pizza. Cook well on both sides - the crust side should be crispy and the cheesy side should be blackened/fried with a melted interior. Utterly delicious.
Despite the attempts above, this question can not be answered accurately without knowing how much (if any) warm Coke you have to wash it down.
My bro calls that “CLOP”: Cold left-over pizza. The breakfast of champions. As in:
Q: What’s for breakfast / lunch?
A: CLOP.
Now that’s disgusting. YMMV of course, but that’s disgusting.
Really, it should be watered down warm Coke and Bacardi from last night.
My first (not altogether joking) thought. I eat pizza every weekend. Half on Saturday, the rest the next day. Freezing for a later time? Bwhaaaaa? I just wrap the uneaten portion in foil and let it cool before sticking in the fridge. Next day I take it out of the fridge a couple hours before I plan to eat it so I only have to zap it for ten seconds or so to warm it up.
Absolutely no offense to the OP, but I’ve never met someone with a pizza dilemma before 
Here’s my personal pizza dilemma. I grew up loving the stuff. For years ate it once a week. Eventually I turned diabetic, though not caused by the pizza. Now I can’t / won’t eat more than a bite or two of any bread any time. It’s been several years since I last had a bite of pizza, and may go the rest of my life without it.
That’s a pizza dilemma.
Thoughts and prayers 
“Now I can’t / won’t eat more than a bite or two of any bread any time. It’s been several years since I last had a bite of pizza, and may go the rest of my life without it.”
Do you need suicide counseling? Life ain’t worth living without a good pizza!
Eat it!
Always wait for food to cool before refrigeration. How you store it depends on how much you have and how fast you plan to eat it. Remember, pizza is good for breakfast, lunch or dinner, and it is good hot or at room temperature. 
Myth: You shouldn’t put hot foods in the refrigerator.
FACT: Hot food can be placed in the refrigerator. Large amounts of food should be divided into small portions and put in shallow containers for quicker cooling in the refrigerator. Perishable foods should be put in a refrigerator that is 40 degrees or below within 2 hours of preparation. If you leave food out to cool and forget about it after 2 hours, throw it away. Bacteria can grow rapidly on food left out at room temperature for more than 2 hours. If food is left out in a room our outdoors where the temperature is 90 degrees For hotter, food should be refrigerated or discarded within just 1 hour.
Regular tomato-based pizza sauce is high acid and will resist bacterial growth longer than, say, a cream-based sauce, but still we all tend to leave pizza on the counter way too long from a food safety standpoint!
The poster is diabetic, I am sure they wish they could eat pizza like a kid. It really depends on what they need to do in order to maintain their own personal blood sugar levels.
And yes, sometimes a diabetic can feel depressed to the point of suicidal when faced with hard choices.
I just close the box and leave it sitting on the table until I’m ready for breakfast.
From a food safety perspective, you’re right. But there a couple reasons you might not want to put it in the fridge while still warm.
If you’re talking about something big like a large pot of chili, sticking it in the fridge while warm can heat up other nearby food. This isn’t an issue for a few slices of pizza, but it’s worth noting.
If you seal something warm with an airtight lid of in a plastic bag, you’ll get a lot of water condensing in the bag as it cools. This can make pizza crust kind of disgusting. Thus my suggestion to put the whole box in the fridge until the pizza is cool, then wrap it up.
I had a friend from college who was convinced this was a prank. He was from Peru, and thought the entire concept of cold pizza was a ridiculous put on from us Americans to fool unwitting foreigners.
Me, I wait for it to cool to room temperature, wrap in foil then fridge it. The foil then makes a nice surface to heat the pizza in the oven, nothing extra to clean. I do like the frypan method as well, but the oven is easier, if slower.
I wait until it cools and then put the box in the fridge. Sometimes I put the slices in a ziploc bag, especially if the fridge is already crowded.
I usually reheat in the oven. Put it in a cold oven turned to 350 and by the time the oven reaches temp, the pizza is ready. If it’s a thick crust pizza, sprinkle a few drops of water on each crust, and cover each crust edge with a small piece of foil.