If you need to touch-up the paint in a room of your home, you might not need to run out to the hardware store and buy a new gallon of paint. Many times, homeowners keep leftover paint in their garage but do not use the paint for touch-ups because they worry that the paint has gone bad. As long as the paint is not too old, it is probably fine to use. Most hardware stores will remix old paint for free. Test a small sample of the paint to make sure that it is still coating surfaces and drying correctly.