Mycology, not much of a shroom fan tbh, but a valuable resource. I never learned it as it seemed pointless as I didn't eat them.
Snow work, I fancy in the future heading for some boreal winter outings.
Primitive camp cooking. Moving away from using modern means to get the most from fires.
Flint napping and in general primitive tool making.
I also want to lace together my knowledge to consolidate it all. I don't know whether I'm alone in this but sometimes I just feel that I lack fluidity. It's the interlocking knowledge I lack mostly.