>>1466410I always got this little pocket warmer with me. It work's great in a a sleeping bag or jacket to keep you warm pretty well.
Those coal sticks can be lit on one or both sides, but I always light both. Even with both sides lit it burns for ~6 hours.
I using it for several years now and it provided me good heat even in freezing temperatures.
And it's super cheap, so always worth a try.