It really depends on where you're coming from--NC is a very long state, east to west.
If you like beaches, you could do Oak Island and Myrtle Beach--get both states with very little driving in between.
Charlotte, NC is very close to the SC border--DH's cousin actually lives in a Charlotte neighborhood where some of his neighbors are in SC, and he's in NC. I'm looking at places that can limit your driving, since you have only a few days.
BTW, NC barbecue is vinegar-based, while SC 'cue is in a mustard-based sauce. If, like me, you grew up eating a tomato-based sauce, I encourage you to try both and see what suits you.