Three cultures as different as possible, plus a general overview, would give the noobs first years the best grasp of what the field is about, so when they become corporate executives, they will have something to regret.

I would recommend Egypt(accept it thus,)Harappan, and what ever pre Colombian civilisation you were most comfy with.
If you spend a lot of time on The Flintstones cave people, you'll spend a lot of time talking about Europe, and they'll come away thinking that it's all about them, because Europe was what happened before there was a U.S.