The next of the Rule of Threes you might not want to violate is being without shelter for more than three hours.

The intact sedan cabin is a shelter from wind and rain in moderate temperatures, but is less able as shelter from temperature extremes.

For cold, it seems to me you would want to scavenge everything that might as as insulation from the rest of the car and to line the cabin. This would include all noise insulation in the engine compartment, the material insulating the cabin from engine temperatures, there may be hood and trunk lining material, also. You will probably want to set aside some material to wrap around yourself. As the scenario specifies the vehicle has some fuel, selective running of the car heating system will work for a while.

For heat, the sedan cabin could turn into an oven. You could put the insulating material on as a cover, expecially to prevent windows from creating a solar oven. It likely at some point you will want to encourage the evaporative cooling effect of your own sweat, so you will set up for shade and airflow by opening all doors. As the scenario specifies the vehicle has some fuel, selective running of the car cooling system will work for a while.

If you needed to leave the vehicle, then the scavenged material needs to become wearable insulation. Use of scavenged wire, thread, or strips of material from seat covers or belts, can become fasterners, thread, or lacings. Think hooded parka / great coat that you can also sleep in / under. For rain and heat, an improvised umbrella might be handy. Door or insulation panels may be light enough to form the basis for an umbrella, though improvising an umbrella frame may be the main challenge. The various door and window operating rods, and various exterior and interior trim pieces, might be light and bendable to be used for umbrella frame purposes.