Straight Dope today: Does a refrigerator cool more efficiently when full?
Basically, the answer is yes. Appears the biggest factor is the amount of cold air that spills out when you open the door. So if you fill up the fridge with any kind mass, there’s less air to get replaced by warm room air.
My quest for more energy efficiency continues! I’m going to put some extra jugs of water in the back spaces of the fridge that even in the most food-flush of times don’t get filled. Actually, I’m running out of kitchen cabinet space, maybe I’ll keep my extra cans of Bush’s Best Chili Magic back there.