Stoupa has around a dozen tavernas and restaurants concentrated along the beachfront and the main road. The food is straightforwardly Greek: grilled fish and seafood, mezedes, moussaka, and souvlaki. Standards are decent given the tourist trade; prices are moderate. Tavernas with sea-facing tables are the obvious choice in good weather. Look for fresh octopus (dried on washing lines and grilled over charcoal) and locally caught fish sold by the kilo.
The Pefko restaurant on the beach is consistently recommended for variety and quality — octopus dishes, stifado, and their "Stoupa chicken" are specialities. Platia Taverna serves reliable Greek standards with a homely atmosphere. Several of the smaller places prepare daily specials based on market produce.