The Exceat Farmhouse restaurant, located next to the Seven Sisters Country Park headquarters at Exceat, is a natural and delicious way to start your walk. It serves excellent home-cooked food (including freshly baked bread and home-made jams) at decent prices, and will also do packed lunches if requested.
Favorite Dish: The English breakfast!
There's an ordinary pub and restaurant at Beachy Head, next to the gift shop. I think it was a Brewster's Fayre. There were seats outside, though, which is quite wonderful on a summer's day.
There is a pub at Birling Gap, which is somewhat overpriced, I presume because of the lack of competition. Didn't try the food here.