The harbour front in Aegina town is lined with cafes and fish tavernas, the best of which have tables directly on the waterfront facing the sea and the arriving ferries. This is where island life happens: Athenian weekenders drinking frappé in the afternoon, families eating late, fishermen selling the morning catch from their boats to the taverna owners directly.
The cuisine is straightforwardly Greek — grilled fish, kalamari, tzatziki, Greek salad, and a carafe of local wine. Prices are reasonable for what you get, particularly compared to the more touristy Aegean islands. Look for places where the fish is displayed fresh on ice rather than pictured on a laminated menu. For coffee, the outdoor cafes along the back streets are quieter than the waterfront spots.