If you live in a really cold winter climate you may have experienced frozen locks in your car door. Water can drip down into the key hole and freeze making getting into your car difficult. Exactly when you really really want to get into your car.
Keep some hand sanitizer handy and squirt some of it in your car door. The alcohol in the hand sanitizer will make quick work of the frozen water in your keyhole. Maybe you already have a hand sanitizing bracelet (50% off link here) which would make carrying the sanitizer on your person even easier.