What are the survival techniques in -20 weather, or even -45 with the windchill?
Layer up, try to cover up as much skin as possible; find adequate shelter and heat. Wear a hat. Body heat starts from the top down.
Wear one of these. Don't walk into a bank or store wearing one, though 😉
Find shelter, bundle up.
Layer up. like two pairs of socks, two pairs long underwear, three shirts, (two longsleeve, one tee) jeans, hoodie, another hoodie, a jacket. stocking cap. Take those (hot hands) packets two of them... and slip them on your toes between your 1st and second layer of socks. Keep your feet dry. change out socks or boots if they get wet. Any activity that gets your heart rate up will increase your core temperature, but it's a double edged sword as it will cool down rapidly when you stop. Stay hydrated and eat small snacks, granola bars ect...
Get into a shelter. A snow cave never gets colder than 32°, and can be as warm as 65° with a small fire going inside. However, it takes work to maintain if the snow is blowing, as you'll still need two openings for fresh air. Line the floor with evergreen branches, blankets or some other insulating barrier. A conical shelter using evergreen branches for the walls can be very dry and toasty, especially with a fire inside. Again, line the floor with an insulating barrier, and make sure your door points downwind. Keep your head covered and your core warm, and don't expose your extremities to cold. Don't take anything that could be a blood thinner, like alcohol or ibuprofen, unless it's medically necessary to keep your heart pumping your blood.
Stay inside. Turn up the heat. We in modern life are spoiled. We would all be hard pressed to survive in a wagon train.
There is a general expression about survival. You can go 3 minutes without oxygen, 3 hours without heat/cooling, 3 days without water, 3 weeks without food. So using that, in the cold you have 3 hours before you are dead. So...#1 get out of the wind. Any wind, even a light breeze lowers the wind chill. A car, a cardboard box, an igloo is better than nothing. #2. Any exposed skin loses heat. It does not matter if it is on your head, arm or leg, it is losing you heat so keep as much skin covered as you can. #3. Make fire. Even if you have to use a bit of gasoline and burn your spare tire, make fire. Besides keeping you warm it can signal that you need help. #4. Call for help but do not try to walk out for help. In the temperatures you noted, you would not last long.
dont go outside