When my younger brother was little, he was a VERY picky eater. PB&J's and chicken noodle soup were about the only things he'd eat. Vegetables? Fergetaboutit! (Or however you spell that.)
My Mom was concerned and took him to the doctor. The doc told her if you're only going to eat one thing, you can't do much better than PB&J. I still hate chicken noodle soup, by the way.