We don't drive to Jacksonville by your route, but I do have a few suggestions for Jax.
The first category of restaurants are the fish camps. Informal, and often fried fish (but not always) In order of my preference:
Clark's Fish Camp
12903 Hood Landing Road
Jacksonville, FL
904-268-3474
(Wonderful Old Florida ambiance - and excellent fish)
Singleton's Seafood Shack
4728 Ocean Street
Atlantic Beach, FL 32233
904-246-4442
Near Mayport Navel Base (and the beaches)
Whitey's Fish Camp
2032 County Road 220
Orange Park, FL 32003
904-269-4198
Haven't been in quite a while.
2) Try Jacksonville fried chicken (especially buttermilk coating, which seems particularly popular in Jax)..
Our favorite was Jimmy's Fried Chicken, but I can't find it on Google, so it may be closed.
The most popular (and it is good) is
Beach Road Chicken Dinners
4132 Atlantic Boulevard
Jacksonville
904-398-7980
3) The most significant ethnic group is Jacksonville are Lebanese-Americans. I don't have any specific restaurants (I saw one called House of Halal, which sounds tempting), but they are worth exploring.
Another place that seems recommended (but I have not tried) is
Hala's Cafe
4323 University Blvd S.
Jacksonville
904-733-1855
or
9735 St. Augustine Road
Jacksonville
904-288-8890
4) For high-end restaurants, my favorite is
24 Miramar
4446 Hendricks Avenue
Jacksonville
904-448-2424