Hi Joe,
a lot of useful hints provided so far by the others…
Here some contribution: handwarmers.
You can get details in the reflector, here:
There are some more threads with related info if you do a search.
I don’t use them very often (not such extreme weather here in Spain), but when I do in very cold days they provide a good way to keep me operational (specially if I need to use my hands out of the gloves).
They could be used as a good way to keep batteries warm? I think so.
Good luck and stay safe!
73 de Ignacio