Living where we do, we have to deal with severe cold temperatures. When my oldest was born, it was July and I didn't think much about the winter. By the time the fall came around, I started to wonder how I could keep him warm in his carseat. I was aware that snowsuits weren't safe (there is too much space between baby and the harness).
Mr.J in snug in his seat
I was gifted an Ottawa Senators carseat cover (similar to a shower cap) and it was perfect. At first I thought that baby would be cold, but I tried it and was amazed at how warm and toasty he was when I took him out.
I made sure to dress him in warm clothing, but found that having a sweater or blanket made him TOO hot.
When Mr. K came along, I still had the carseat cover and used it once again. It was a wonderful accessory to have.