If your vehicle does not have air conditioning, but you have a work refrigerator, you might consider getting a short sleeve canvas vest with pockets, and putting refreezeable “blue ice” packs in the vest pockets. There are special vests, but a “Quail Hunting vest” is very similar and can be found cheap at second hand stores. The blue ice packs can be too cold next to the skin. If so fold wash cloths into a spacer.