Marina di Campo's restaurants follow the Elban pattern: the emphasis is on seafood, the local wine shows up everywhere, and quality correlates loosely with distance from the beach front. The harbour area has the highest concentration of places to eat, ranging from good trattorie to tourist-facing pizzerias; for better food at better prices, explore the streets one or two blocks back from the waterfront.
The local specialities are the same you will find across the island: cacciucco (a dense Livornese-style fish soup), grilled or fried anchovies, and pasta with seafood. For meat, the Elban tradition leans towards grilled pork and wild boar stew — Campo is close enough to Monte Capanne's chestnut forests that the game is genuinely local. Finish with schiaccia briaca, a dense cake made with pine nuts, sultanas, and Aleatico wine. The sweet Aleatico itself — a red dessert wine indigenous to the island — is worth trying on its own.
The harbour is a working one, and a few boats still go out at night; ask at the fishing quay in the morning and you may be able to buy directly from whoever just came in.