@ Mouse,
I agree with the more linear skill sets (e.g. chemistry and pottery or even brewer). Could be argued a Farmer has multi-disciplines.
That is one aspect I have tried to look at myself objectively, do an assessment where I need to improve, or if I cannot gain those skills, whom is around me who can.
I always think of the Certified Network Engineer, or Windows Security Expert, and what post-SHTF skills they have that can be of value? Can they teach math?