Most of the people working in technical jobs at computer company startups have a CS background, though some have other backgrounds (occasionally no formal college at all) with self-education in CS. However, business school backgrounds (including CS+business) are rare to non-existent among those working in technical jobs (as opposed to non-technical jobs like finance, accounting, marketing, etc.).
Some economics, finance, and other social science type courses may be interesting and useful, but adding a full business major probably not (and may send the wrong signal to some employers).