Heat loss from radiation is bigger than most people think. Sleeping under the stars might be romantic but the twinkling little beggars will suck the heat right out of you.
(space is a very cold place)
If you can shelter under a spruce you can save a lot of heat from being radiated into the night sky, so a tent, a tarp or even one of those emergency blankets to rig as a tarp might help.

Thermarest and the other pads are not enough by themselves but it helps a lot if you put down a layer of brush and/or grass first.

Metal bodies like cars and planes suck a lot of heat and radiate a lot of heat into the night sky too.

It is surprising how much of a difference being able to camp under something makes, even just a tarp set up as a lean to will give you cover from the sky and a windbreak.


If you are forced down:

Staying near the plane is good.
Try to keep it clear of snow and keep a good fire going if you can.

Keeping snow off the wings makes the plane much easier to see.
If it is shiny outlining it with brush on the ground might help.

Even a small fire can be seen from a long way away at night, but wood smoke is a disappointing signal during the day.

Smoke looks too much like mist or fog and usually the fire is too small to punch the smoke above the thermal inversion layer and into a nice tall column.
Having material like motor oil or rubber from the plane to burn that gives black smoke might make a difference.
Just be careful not to blow yourself up trying to burn it.

Having one good fire instead of three small ones is fine.
If they are looking for you they will investigate a single fire just as quickly as three in a group.

If you can torch an isolated spruce tree you might get yourself found by the fire watch instead of the Search and Rescue teams.

Try to make sure any electronic signaling devices are working.
You might be lucky and have a working radio, or location beacon, but sometimes they get their power leads or antennas ripped loose.

The plane itself is a source of emergency gear too.
It will be loaded with fuel, metal, wire and cushions useful for insulation.
Plus there is whatever the plane had in it, both the emergency supplies and the cargo if you must.