I'd always heard that "cracker" is an old southern term from working class redneck. It seems the men who drove mule teams pulling wagons (the original TRUCK DRIVERS) were known as "Crackers" for the whip they had to use.
I never heard it was associated with the coastal areas...just in the South generally.
It's funny, all these old theories for the term "cracker". The most likely origin is that "cracker" probably comes from the Gaelic word "craic", meaning bantering, bragging, and boisterous conversation. Cracker was a term used in Shakespeare's day, long before Southern crackers existed.