With a seat heater. They were popular in the old times, when engines were not digitally controlled and took a long time to heat up enough to provide any warming effect inside the car.

Also heated thermal underwear [1]

[1] - https://www.amazon.com/J-Jinpei-Lightweight-Intelligent-Temp...

Every car I've been in in Norway has had heaters in at least the front seats. The Tesla S has rear seat heaters as a configuration option when you buy the car as well as an option for a heated steering wheel. Quite a lot of the cars I rented in the US had heated seats, even in North Carolina.

Heated seats and steering wheels.

Dress properly for the weather.

With clothing.