Things keep better at low temperatures! Not always… You should be careful, no matter how weary you are at the end of the day, of leaving medication, eggs, jars or cans of food, and especially any fizzy drinks in the boot or on the back seat of your car… Some foods and pharmaceutical products may have nasty surprises in store for you in sub-zero temperatures.
http://www.slate.fr/story/199332/objets-pas-oublier-voiture-geler-froid-danger