I always keep a plastic grocery bag or small, bathroom-sized trash bag in my car. I just thought it made good sense to keep a junk receptacle within easy reach to keep my car from becoming a tiny landfill on wheels. One night, driving my [very intoxicated] friend home from an evening of wedding festivities, rich food, and numerous mixed alcohols, I realized the true lifesaving aspect of having a bag in the car. My dear friend was able to vomit sans mess, and without me having to pull the car over in a questionable area of an unfamiliar town. Always keep a trash bag in your car -- it might save you a highly unpleasant mess in the future.