We were visiting the ruins with a guide and lunch was included so we went to the buffet at the Sanctuary Lodge. There was a large selection but on the whole I was disappointed. The room was very noisy and seemed more like a canteen than a restaurant in a five star hotel. There wasn't enough space between the tables, so it was hard to get to and from the buffet. And we only wanted a light meal so we paid a lot of money for not much food!
If you have a choice and like us just want a snack I'd recommend that you go to the snack bar or bring a picnic from Aguas Calientes.
Obviously, if you sign up for a guided trek of the Inca Trail, all your meals will be prepared for you en route. It makes for a nice departure to normal backpacking, where you have to cook and clean up for yourself. Once you arrive in Machu Picchu, there are some expensive restaurants and also a small cafeteria, which serves pretty tasty if a bit pricey food. It is far cheaper to eat in Aguas Caliente, where you will catch the train back to Cusco.
Favorite Dish: Food on the trail was generally good, ranging from fried fish the first day to spaghetti. In general though, it never seemed like enough. You burn lots of calories on the trail and need more food than you would normally. Bring extra stuff with you for sure! The cafeteria in Machu Picchu had a really great chicken salad sandwich but you will want another as soon as you finish it. In Aguas Caliente, there are numerous street stalls and in the main market, very cheap and tasty local foods. This picture is of baby beef heart kebabs, served on a stick with a potato on top. Sounds gross but really great. And at 30 cents, tough to beat.