I was stationed at Eglin AFB (Ft Walton Beach/Destin area) back in the 90's. If you like sea food, follow where the fishing boats come in and dock. The main drag along the coast will have the chain restaurants but those even those chains had good sea food. Where the fishing boats dock, will be some of the finest and freshest gulf seafood that is amazing.
If your headed down to Destin via way of Nashville your probably running interstate 65 to Montgomery. In Montgomery you catch a two lane (used to be 2-lane anyways), I believe is rt 331 through lower Alabama and the Florida panhandle. As SJB noted, that two lane will run you through a couple little towns. I would stop at the small little mom and pop restaurants and I always walked away with a good meal.
Also, when travelling that little 2-lane route from Montgomery to Florida, watch your speed. Those cops in those little crossroad towns are looking to nail you for speeding especially if you got Yankee plates on your car.