Here's what each farmer specializes in:
* Mr. Boggis: Chickens and ducks
* Mr. Bun: Geese and turkeys
* Mr. Bean: Pigs and apples (he also has a big orchard)
So, the farmers primarily eat the products of their farms: eggs, meat, and apples. They are also likely to eat other foods from their local area, but the story focuses on their farming activities and their frustration with Mr. Fox.