A country breakfast, or farmer's breakfast, is meant to be big and filling. It's a high-calorie meal that can include eggs, hash browns, steak, sausage, ham, bacon, pancakes, grits, gravy, or more. It's traditionally meant to fill you up and give you the energy you need for an early start to the day on a farm. Even during the Depression, farmers got a jump on the day with these hearty meals.
The beauty of a full English breakfast is the variety of tastes and textures all found on a singular plate. While it's not a light meal by any means, it's a substantial and filling way to start the day - so it's no surprise that John Lennon favored the hearty meal that would keep him full throughout his time at protests, rehearsal, or in the studio.