Rincón eats fish. There are no fancy restaurants — instead, a string of family-run cantinas along the beach serve red snapper (pargo rojo), sea bass (mojarra), prawns, shellfish, and the local crab in coconut sauce. The usual sides are coconut rice, fried plantain, and a small salad. A whole grilled fish with sides will cost a fraction of what you would pay in Cartagena.
Look for the cantinas where the locals eat at lunchtime — generally a sign the fish was landed that morning. The best are at the southern end of the beach. The town also has a couple of small panaderías and a fruit stand near the bus stop. Bring cash; very few places take cards.