Originally Posted by becnal
Put the pizza in the box and the box on your back rack. The springy mouse trap thingy will hold it in place. I do that all the time.
If you don't have a springy mouse trap thingy use bungee cords. Keep bungee cords on your back rack, they will always come in handy. A back rack is absolutely essential to car-free living with a bicycle IMO. Failing bungees, raid string from the office. Lots more options if you ditch the box.