I use a battery powered hand warmer in my coat pocket as necessary.
Recharges via usb in the truck. RGS gave them out to sponsors.

It really depends on your circulation.

Thin fleece, wool, or silk work pretty well for me.

I have a pair called “Hot shots” I found at Menards in their hunting dept that seem to be adequate. Nice orange, so harder to lose.

Out there doing it best I can.