Will 5 pizzas in the same Hot Bag stay warmer than 5 pizzas in 5 separate Hot Bags? For example, say I am delivering 5 pepperoni pizzas to 5 different addresses. In one scenario, I Keep all 5 in the same insulated Hot Bag, I carry that bag to the door, and I quickly remove one of the pizzas from the bag to give to the customer.  In the other scenario, I use a separate Hot Bag for each pizza. This would mean that only one bag would need to be opened while the other 4 bags could stay closed.
Which method would keep the pizzas warmer?
 A: My guess is it's best to put each pizza into its own insulator, but then stack them for transport so that the stack has the same size and surface area a larger insulating container would have.
Stacking the boxes in transport minimizes heat loss since it's proportional to exposed outside area.  Opening a container would let significant heat out, so that should be avoided.
Even better would be to make some insulated structure that you put the pizzas in during transport, each in their own insulated container.
A: I don't think there will be any difference. Provided the bags are ideal insulators and the pizzas are at the same temperature, there will be no exchange of heat. Even with all of them in the same bag, there will be no exchange of heat as no temperature gradient exists!
A: If they were ideal insulators, the 5 separate bags would be better because you wouldn't have repeated heat loss from opening the same bag 5 times. Primarily this heat loss would be in the escape of hot air, exchanged for colder outside air. If the hot bags were extremely poor insulators - effectively as if you weren't using any - then you'd want the pizzas stacked on top of one another to minimize the exposed surface area.
You can combine the advantages by just transporting the 5 hot bags stacked on top of each other.
A: With the two options, the temperature difference and bag insulation R-factor are the same. 
The five-bag option has five times the surface area (if truly "separate" and not stacked).  So the one big bag should be the better choice.
A less snicker-inducing version of the "two people - two sleeping bags - how to keep warmer" problem...
