Aw man, they are so lucky someone like you cared enough to go in the store and find them to relieve the dog. I would bring cosmo with me in the car only a few times but in Winter or early Spring because too hot in Virginia! He literally would wait in the car 5 minutes at a time while I picked up my daughter but I felt guilty about that so usually I would just carry him in, or under a shirt or towel
I know too well what can happen in a hot car.