I mean thinking of a typical non specialized business BA here (Germany) the math and statistics classes are pretty useful, as is the basic economics primer. The required law courses and tax related courses are pretty useful. Accounting, finance and controlling are useful as well and so are marketing (mostly math/data analysis), strategy, project management and production management (usually operations research centric but also covers quality management). HR seems fairly meh unless you want to go into HR (as the most relevant stuff is already covered in law).
The typical electives cover more in depth of the above and sometimes business information systems, psychology, programming and the like.
And there's some other stuff that's pretty useful like negotiation classes or case studies (if they cover interesting topics).