My go to breakfast prior to a big (~4 hour) ride is 500g or so of baked sweet potato, cinnamon, salt, ground ginger, some chopped walnuts (or hulled hemp seed), a scoop of vanilla whey protein, and plenty of coconut milk. It turns out to be 6-700 calories with plenty of carbs, some good fats and a bit of protein. That and some black tea (Irish breakfast, please) and I'm good for quite a while.