So much to do at MB. From charter fishing, to scenic boat tours, parasailing, helicopter rides, Shagging / dancing, Amusement parks, mini golf. Alligator Adventure.
And as mentioned Wilmington, and Charleston. It all depends on where you are staying as to which is a longer drive. From MB proper, It is 1 hour 30 min to Wilmington, and 2 hours to Charleston. But that's not the whole story. Southport is between MB, and Wilmington, and of course the WORLD famous Britt donuts are at Carolina beach.
There is history all around you. From Fort Fisher, and the Orton Plantation, and Brunswick Town near Southport, Not to mention Historic / Wilmington itself, To Charleston, with Boone Hall Plantation, The Battery, Patriots Point, and well there is just too much to mention.
You are right in the middle of more to do than you have time for.
BTW. You can drive on the beach at Fort Fisher IF you have 4x4. Also on the North End of that island.
You like Hiking. Hike up the beach to the state park, or to town. Or to the pier at Garden City. No reason at all to be bored at MB.