Algorithm Complexity (the basics: you don't have to know everything about every sort algorithm, but if you understand the basics, you will avoid many mistakes that many developers make, because you will know WHY some code is less efficient than others -- and when it matters)
Functions: Functions are in all languages. Understand things like function purity (when and why it matters), idempotency, etc.
Thanks Patrick.
I can see how they can be used as new technologies are invented/discovered/created as they are the basics as @rhymes pointed out.