Classes I took that have really come in handy over the years:
Theatre History 1 & 2, Scenery Design, Lighting Design, Art History, all of my History classes, German classes (great for doing Brecht and Faust and WW2-centered shows), Piano, Voice, Acting, Rendering and Drafting, Sound Design, Red Cross First Aid, EMT, Directing, Script Analysis (don't remember the real name--great book: Backwards and Forwards by Ball), Stage Management, Accounting, Computer application classes.
Classes I wish I had taken, but didn't know I should have:
Music Theory, Opera Appreciation, Stage Combat, Physical Movement, Drawing and Drafting, Intro to Psych, Costume History, Stage craft, Make-up, Automation (didn't exist when I was in college), Physics of sound, Playwriting, Videoediting, Photoshop (didn't exist at the time), basic electronics.
LOTS AND LOTS OF PRACTICAL EXPERIENCE IN EVERY TECHNICAL AREA, INCLUDING FRONT-OF-HOUSE.
DIRECTING AT LEAST 1 SHOW FROM START TO FINISH.
ASM'ING AT LEAST 3 SHOWS UNDER DIFFERENT PSM'S AND DIRECTORS
PSM'ING AT LEAST 2 SHOWS. (That way you learn what you did wrong the first time and are able to improve the second time.)