Nothing will keep a person feeling full longer, or keep energy levels more consistent through the day than a meal rich in protein and fat.

When I eat a breakfast of steak and almonds as I have been lately, I can have it at 6:30 am and not even start to feel hungry until around 1-2 pm, and I'm full of energy all day rather than crashing mid-morning. Cereal can't do that. Honestly, a generous plate of bacon and eggs would be more satisfying in that regard.