I'll give you two places that were my favorites.
1. Checker barbeque, 3566 Saint Augustine Rd. has GREAT mustard based bbq sandwiches.
2. Seafood Kitchen, 31 Royal Palms Dr. Atlantic Beach (just off Atlantic Blvd). They have a nice restaurant that serves a good meal, but for value, go to the takeout window on the back side. Same food but you'll save some money.