San Gimignano's dining scene punches above its size. You're in classic Sienese country, so expect ribollita, pappa al pomodoro, wild boar ragu on hand-rolled pici pasta, and plenty of local Chianina beef. Vernaccia di San Gimignano — the town's DOCG white wine, one of Italy's oldest documented wines — is the obvious accompaniment and appears on every table.
The piazzas fill with tourist restaurants, some of them fine and some of them operating on a captive-audience model. Walk half a block off the main drag and the quality improves and the prices drop. Lunch is generally better value than dinner, and booking ahead is wise in summer.