I will second the recommendation for Sete. Great, simple seafood in a crowded, family place. We made new friends. This was for my honeymoon which was 20 years ago, so I do not know the name of the specific place, but there were a number of similar choices down by the harbor.
Carcassonne is a tourist joint, so I would not look for anything exciting as to food there (though it sure looks cool). Aix is the place where you will get the best chow, but I would just rely on my chow instincts (which means I do not know any places), and recs you can find. If you have not, I would also post the query on CH.
If the itinerary was not set, I would suggest you skip Bordeaux and the Cote d'Azure and explore Perigord. Better food, prettier countryside, amazing history, etc. And you would be there in full truffle season. The down side is that the rivers would be at low water level, so the rides through the gorges would not be as much fun as in the spring.
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Feeling (south) loopy