In Does a refrigerator cool more efficiently when full?, Uncle sez, “decide what you want beforehand, then get in and out fast.”
Now sometimes I have to move more things in/out of the fridge than my two hands can carry at a time. What’s more efficient: (a) keeping the door open while I make multiple trips, or (b) opening/closing/opening it again? Excuse my grasp of physics, but does (b) push out cold air when the door closes?
Not significantly, but when you open it cold air spills out the bottom and warmer air replaces it from above. Mind you this happens continually when you leave it open too, so yes, closing it at all possible times is the wisest strategy; apart from all else, every now and then you are not going to get back to it as quickly as you thought and your electricity is spilling all over the ground while you pick up that dropped shopping bag (or whatever).