Finance I, II, III. Accounting I, II, III. Corporate Strategy. Emerging Markets. Micro/Macro Economics. Business Acting. Marketing Strategy. Ops Research.
I did online classes. Read books. Still signed up for an MBA after I realized I didn't have the confidence and needed time to develop in an environment that encourages immersion and discussion of these topics.
Not everyone needs to do this. But those who do, like me, should do an MBA.