Winter car seat? What to wear! [On]

My baby is currently 5.5 months old. He will be 9 in December. I am in SW Ontario and wondering what you do for winter clothes.

I understand that you shouldn't put a snow suit on your baby in the car seat, should do layers blankets and then possibly put one of those covers over the car seat for warmth.

My concern is when we go shopping, such as groceries where he is sitting in the front of the cart, or running into the mall. What do they wear?

I can't imagine taking him out of the car seat, somehow wrestling his one piece snow suit (which they all seem to be) on him, then taking it off again in the store.

Tia!