A breathable thermal is a good idea; long johns work well. Over that, a thick sweatshirt, and on top, a Gore-Tex style shelled jacket. Ideally it should be weatherproof. Gore-Tex is great because it releases moisture without letting in any. Good gloves are equally important — we lose the most warmth from our face and head, our hands and feet, and our core. So when you have insulated boots and gloves and a few layers around your middle, the only part that can go unprotected is the face.
Face covers, the kind skiers use, are a great winter bike supply. Many Gore-Tex shells zip up entirely to cover the nose but this may not be as comfortable as the soft easy to breathe in face covers.
After you’ve protected your body, protect your bike. Keep your bike clean with bike supplies such as chain lube. Make sure your brakes are tight. And when biking in inclement weather, take extra precaution. Try to wipe your bike down after getting it wet. Bike supplies can help you stay warm and keep your bike clean, ready to see another season.