Remind him to keep liquids that could freeze/burst/thaw in the trunk or left in the car overnight, in something that will contain the liquid and keep it off his other items, you can put them in something like freezer bags.
Remember that an ice chest makes a nice box to help prevent freezing and wide temperature swings for liquids, drinking water and electronics and fruit, and batteries, as long as everything is kept safe from the freeze/burst/thaw cycle.
Thanks for the ideas.