During your schooling, what one or two classes would have been most beneficial for you in your career? Whether is was secondary or post-secondary education,, I find many people wish they had taken X or Y instead of something that seemed interesting at the time.
For me, it's an odd coupling of accounting/budgeting/finance to help me read & understand & act on much of the financials in my work. Another would be, philosophy, in order to better guage the signs of the times and anticipate directions for acquiring books we publish.
What are yours?