Mens Thermal Underwear
Mens thermal underwear can be a real life saver in the cold. There are light weight for cool times, medium weight for colder times, and heavy weight for very cold (more like sub-zero) times. Hypothermia is not something you want to have happen to you or members of your team.
You want the moisture to be wicked away from your skin. This will keep you drier and warmer. You do not want to be wet out in the cold. This is when hypothermia can set in. This is another reason why you do not want to be out by yourself. Always use the buddy system outdoors.
For those times when warmth is needed quickly, a high BTU backpacking stove can come in real handy. Your best bet is to always be dressed correctly for the weather you are going to be in by having the correct weight of mens thermal underwear.