You need to have a light breakfast only. There should be a bit of protein and carbohydrates and that should be enough. I would normally eat an egg and then a piece of bread plus half of a banana and that's usually enough to keep me going from like 5:30am to 9am. If you eat too much, your body will feel sluggish and your endurance is consequently affected. On the other hand, if you eat too little, your body will get exhausted easily and it will feel like your body is not having proper blood circulation. You wouldn't want any of these distractions during biking.