If you’re headed to a remote area, you might not have reliable access to water and won’t want to waste the precious liquid you’re carrying. Leaving a wet towel laying around overnight could lead to mold or mildew, but a few hours in the car shouldn’t hurt it. You can wet it at home and store it in a sealable bag. If you have a significant trip ahead, plan to pack your towel where it’s easy to access and wet it at a rest stop, gas station, or another available bathroom later on in your journey.