You do work when you lift the pizza boxes. You do NO work ( in the physics sense ) when you carry the pizza boxes. WHY?
I know the answer, but have a similar question myself...
You do no work against gravity because you are not moving any distance (more accurately displacement) in the direction of the force i.e. the force and displacement are perpendicular once you have lifted the boxes.
As work done = force x displacement parallel to the force, no work is done. (The equation in its proper form is