In addition to double socks, I have been using those single use toe warmers between the socks at Rally Sweden: https://www.amazon.com/HotHands-Toe-.../dp/B0007ZF4PE
They have also set for gloves which I used too some times when there was windchill: https://www.amazon.com/HotHands-Hand...ZM2Y2E9D1E1S04
I'm sure each fisherman shop is selling them all around the world.