What about a coat you can use camping (at night) that has heat-elements in it?
4 uses - indoors, in car, on motorcycle & mobile - 12V heating Vest
Men's heating Vest - with 2 pockets outside & 2 inner pockets for battery
Resisting wind & water from outside and absorbing moistures from skin.
12VDC Alloy Heating:
Soft, fleible, safe, washable Alloy heating element. Temperature range from 100 F to 155 F
Handy li-ion battery set with 5 scales temperature, intellgent temp. Sensor controlor.
Battery endurance time 4-14 hrs.
It is rechargeable by the power source from house or car(dc 12V) and has no memory effect.
It is durable for over 500 times. It weigh 202 gm only. easy to carry.