From an article in the February 2015 issue of Outdoor Photographer, page 54:
"Years ago, cameras had to be taken apart and prepared for cold weather or they would fail. That's no longer true. All cameras today can function just fine to temperatures well below zero, except...
Batteries quit working as the temperatures drop. They will work fine again once they warm up. I keep extra batteries in a pocket in my jacket with a handwarmer. You could keep an extra battery in a pocket next to your body, but exchanging batteries will be painful.
Condensation is a big problem with cameras, so never keep the camera next to your body. Even in winter, your body puts off a lot of moisture, which will condense on a cold camera body. Also, never bring an exposed cold camera inside a house or a warm car because serious condensation can occur, which can mean camera failure and shipment to a repair location. Put your camera away inside a sealed camera bag or a plastic garbage bag until it warms up.
A cold camera is a good thing when it's snowing because the snow can be brushed off without it melting. But never blow off snow with your breath or you'll add a layer of condensation, which is really a problem if that happens to be on your lens.
Warm clothes in layers are key, along with good, insulated boots, flexible gloves and a warm hat. Warm, insulated boots are very important because, as a photographer, you'll be standing a lot as you set up shots and wait for the light. Cold feet will send you home quickly.
For gloves, check out hunting stores. Think about it, a hunter needs gloves that are both warm and flexible, plus they usually have some sort of gripping material to allow you to grip things (such as a camera and its controls). Growing up in Minnesota, I never found "half" gloves or mittens that exposed fingers useful. Cold camera bodies and tripods were way too brutal for bare skin.