I am going to visit Lapland soon, and coming from the warm climate of Israel, I am sure to feel the cold.
In addition to buying a good coat and other gear, I also bought warming pads. Specifically, http://body-warmer.com/ where it says that it is "Made from wood and iron powder, Non-poisonous, not flammable".
But I'm not sure if these would be possibly to bring on the plane with me. Especially since I usually try avoid checking my bags, and pack very lightly so I can take everything with me as a carry-on.
(If it matters, I will be flying with both Ukraine Airlines and Finnair.)