In many cases it is the little things that turn out to be the most important items. That could be said about keeping the gas tank of your vehicle as full as possible in the cold winter months. When your tank is low, that allows more air into the tank. Air carries moisture which can cause condensation in the tank and the fuel line that leads up to the engine.
If the condensation, which is really just moisture, freezes, you can have some difficulty getting your vehicle started as well possible problems with the overall operation of the vehicle occurring. When your gas tank is full, or nearly full, there is less air, thus there is a smaller chance that freezing will occur. As a precaution, it is even good to periodically fill the tank with small amounts of fuel from time to time. This will go a long way to preventing any mishaps with a less than full gas tank.