https://www.amazon.com/WORLD-BIO-Warmers-Disposable-Adhesive-Backing/dp/B01N8QBSTX/ref=mp_s_a_1_1?ie=UTF8&qid=1543526691&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=world+bio+body+warmer&dpPl=1&dpID=51uPS0gCl0L&ref=plSrch
Keep your core warm and it will take care of your extremities.
Also carry a small flask of whisky. Helps a great deal. Just don't use it in a life or death situation. And make sure your core stays warm.