There's not enough info to answer this. What's your goal? If your goal is to maintain your weight, then match your calorie intake to your calorie expenditure. So, if you can estimate how many calories you're going to burn in those 2 hours. If you have been maintaining your weight, you need to eat as many calories as you burned during those 2 hours in order to continue maintaining your weight. If your goal is weight loss, then it's pretty simple in theory: You must create a calorie deficit (burn more calories than you eat). However, this is nearly impossible on a daily basis for the average person. Currently, it requires a certain daily calorie intake to maintain your weight. If you want to lose, you need to consume less calories. One pound equals 3500 calories. In order to lose one pound a week, you need to reduce your calorie intake by 500 calories OR increase your calorie burn. (or a combination that creates this deficit) As far as breakfast goes, you should always eat a healthy breakfast but the size is irrelevant. The calories you consume should be spread out across the day. The latest recommendation is to eat 6 mini-meals a day (or 3 meals + 3 snacks). Each meal should have a bit of low fat protein, carbs and you should eat plenty of veggies and fruits during the day.