San Ignacio is small enough that you will eat in the same handful of places. The food is broad-Peruvian — arroz con pollo, lomo saltado, soups, plenty of yucca and plantain alongside the rice. The local distinction is the coffee: locally grown arabica is sold by weight in several roasters, and the small cafés around the Plaza de Armas serve it properly.
Restaurante Yuradi does a reliable menú del día — three courses for around 10 soles. La Casona is a step up in price and quality, with a longer carta of grilled meats and fish. For breakfast, the small cafés around the plaza serve huevos con jamón alongside fresh juice (pineapple, papaya, maracuyá) and good coffee from Industrias Cafenor.
Local sweets are worth trying: chancaca (raw cane sugar fudge) and bocadillos (peanut bars) are the regional snacks, sold by weight from small shops on the main streets.