As stated by Jeff M, lifeboat rations should be fine, and there should not be many other types of food that will last better. When you consider that these rations are designed to be stuck into a compartment on a lifeboat, for a few years, they will hold up to what happens in your car. A lifeboat is going to be as exposed to elements as you car, but the elements are probably going to worse for the lifeboat's environment.