It's not difficult to keep your dog comfortable in the car while you go off to do something.  Generally speaking, if it's over ~65f outside and you know it will be longer than 5min, leave them home.  Otherwise, crack the window a little and don't park in the sun. Just think, fatty here is just too lazy to do even this much for the family pets. It's 20-40f here right now so I tend to bring the dogs everywhere, they love car rides. And walks in the snow are great fun for them.