Most useless thing:
Progressive Theory of History
Sociology

Fortunately, we also had Latin and Greek and read real history in original languages.  I wrote a small language model (all the buzz phrases uttered by the teacher in a Random Transition Network) to write the sociology papers - and got B+.

Most useful things:  
Linear Programming (e,g. optimize ratios in a mixed berry product).
QR Factorization (fit non-linear models to datasets)