Some gravies do not freeze well, such as those types with milk or dairy products included in the ingredients. But yes, you can certainly freeze any leftover broth-type homemade gravy you have. Put the leftover gravy into an airtight container and freeze for up to a couple of months. When ready to use the gravy, take it out of the freezer the night before and put it in the refrigerator to thaw. Reheat the gravy in a microwave-safe bowl in the microwave, or in a pot on the stove until heated through.