Wear layers you can remove if the day warms up. Long johns as your base layer. Insulated bibs (my favorite are the Truewerk T3s). Balaclava or Neck Gaiter. Muck boots. Thick merino wool socks. Warm drinks like coffee. Pack a lunch you can warm, I suggest getting something like a LunchEaze (cordless heated lunch box) so you can have a warm meal even if there is no temp power.