What is the most useful skill that I can learn to make myself more employable as a business major? Ex: Computer programming, MIS, SQL.
Advanced Excel - pivot tables, database functions, analysis tools
Communication
The ability to do well in an interview. That means appropriate dress, a firm handshake, a grasp of small talk, the ability to talk yourself up without sounding cocky, real knowledge of your field, humility, and good manners when it comes to follow up after the interview.
I agree with Advanced Excel and interpersonal skills. Work on eye contact, and interacting with professional adults. We like to see adaptable, mature early career candidates who are not wallflowers and who are eager to learn.