I'm not exactly sure how much they eat, but I keep food and water avalible to my chickens all the time. If they are free ranging then they won't eat quite was much. Chickens do drink alot. i have 9 hens and they drink 1 gallon a day.
Mine free range all day. They eat very little of the layer mash I leave out. I give small amounts of treats. Mostly they find their own food. Don't know quantities, sorry. Some people do keep records, though!