Not much there...
If you're lucky, there is a cornell bbq chicken stand just south of town, on route 14. Not to be confused with Mr. Chicken, in town.
Capt. Bills on Seneca Lake is a nice view, but pricey.
For the better breakfast (never been there for lunch, since I'm always driving at the track during lunchtime), try Savard's Family Restaurant in town.
I would never go to Watkins Glen for the food.