Refrigerators and freezers work best if they are nearly full, but there is room for the cooled air to move around the food. In the freezer you want to be sure you don’t block the temperature sensor. If yours isn’t full, you can fill plastic containers such as milk jugs or water bottles with water to hold some space. The water will expand as it freezes. Leave an inch or two at the top to allow for that.
In a power outage, the frozen containers serve first as an ice block for preserving the food, and then as a water source. Cold containers of water in the refrigerator help the unit to cool back down more quickly after you have opened the door. Keep liquids covered.
I filled two-liter soda bottles with water and rolled them to the back of the lower refrigerator shelves. This helps the refrigerator work more efficiently. It also prevents foods from being pushed to the far back of the shelves and forgotten. I can put in more or fewer bottles of water, according to how much empty space there is.
For the best food safety, the refrigerator should be between thirty-five and forty degrees Fahrenheit. According to one article I found, keeping it ten degrees colder than that will use 25% more electricity. And freeze your produce! I put a thermometer in the refrigerator and learned it was 32° F. I set it one number warmer on the temperature dial and it became 35°. I’m not going any warmer, because I want to keep my food as fresh as I can for as long as I can.