Useful Classes and Practical Skills
Graduate school, by and large, and with the possible exception of Med School, is not about taking classes. Those letters "Ph.D." mean you’ll be a doctor of PHILOSOPHY, not of chemistry, or molecular genetics. The philosophy is the philosophy of independent inquiry. Learning to learn on your own and to conduct research into the unknown is the name of the game. Nonetheless, there are in fact classes and skills that even an advanced grad student or post-doc can take or learn that will be immensely practical for a future career as a technical professional.