If you are a little salty about the whole delivery boy side of this game, getting orders to deliver pizza can be a bit of a kick in the nuts. When you get your first pizza delivery order, yes there are more than one, you will be told that you need to keep the pizza box flat otherwise it will damage the contents. I guess it makes sense.
If you load the cargo you may find that the box ends up sideways on your back. Hold it in your hand and it will also start to take damage because it is also on its side. How do you carry a pizza box flat so that it does not take any damage when you are moving it?
Your options will depend on where you are in the game. The most basic solution is to fill your inventory with more stuff. If you have ever filled your backpack with cargo, you will know that once your backpack is full, items get stacked on top. Most importantly they get stacked flat. This will allow you to carry a pizza box flat and avoid damaging the cargo.
If you are further into the game you will be able to use a vehicle to make this easier. There are no pizza bikes sadly but you can load them flat into a truck or also use a carrier. Whichever works easy for you.