Wind proof gloves, thermals, a good windproof coat, wind proof beanie with built in balaclava (you can pull it under your chin when going into 7/11), good heater and the best thing are those disposable hand warmers. They come in various sizes, you can sit on the ones that are made to go into shoes and they are cheap. I put extras under the passanger seat. I've driven for hours in freezing weather with this setup. I have brooklands, no doors or tunnel cover. High quality snow board pants work well too, might get too hot if you use the heater though.
Rod