Midweight Baselayers are excellent next-to-skin layers when in cold environments.

In extreme cold envrionments, your L3 will keep your core insulated and warm while both static and active.

A softshell with fleece lining is really the ultimate shell layer when dealing with extreme cold. A durable outer shell protects you from frozen terrain and an inner fleece laminate helps trap heat.

Once you're done adventuring around on foot, your core body temperature will begin to drop. It is important to retain as much heat as possible so once you become static (not moving around), pop on some L7s and keep yourself warm.