There are a plenty of restaurants near the exits of the complex, inside and outside of the park and in the hotels in San Juan Teotihuacan as well as grocery stores and bakeries. Consider having one prepare a picnic for you and enjoy it at the park.
Restaurante La Gruta is located on the eastern perimeter around Teotihuacan, 500 meters down the road across from the "Puerta No. 5" entrance. The restaurant is located deep inside a subterranean cave and illuminated by two large holes on the side along with other ambient lighting. There is a bar with a vast selection of beers, wines, and liquors. Prepare for the possibility of a serenade by a small Mariachi band or weekend shows featuring live Aztec dancers.
Hotel Villa Arquelogica of Teotihuacan is located inside of the park and close to the entrance it has a very pleasant dining room serving 3 meals a day. It is reasonably priced, food is excellent and the staff very helpful.
Museo Teotihuacán, The museum at the park has a restaurant.