On a snowy or messy day, you can easily go through half a gallon or more of windshield washer fluid trying to keep your windshield clear. For that reason, it's also a good idea to keep some extra fluid in the trunk in case you run out. And make sure you get the good stuff - stay away from the already-half-frozen stuff outside your local gas station! Even though it may say "Good to Minus 30," some of these cheap fluids freeze around zero degrees! Even if you buy the good stuff, if you live in a very cold area, you also may need to supplement your windshield washer fluid with some concentrate. The concentrate is available in one-pint bottles and works very well at extremely low temperatures.