Preparation For the Big Run
The Early Preparation
Preparation starts many weeks before the event. You need to know some of the basics of the race like: what nutrition will be provided on course, where are the feed stations, and what are the weather conditions likely to be. You may not be able to influence the weather, but you can prepare for the conditions. Finding out what nutrition is going to be handed out is important too because it would be a good idea to practice with this nutrition and make sure you can tolerate it and you can adapt to it. If you can't tolerate it, it is better to find out weeks in advance than on race day.
Train Your Race Plan
The first step is to figure out what nutrition works best for you. This includes not only products, but timing as well. Start doing this 10 weeks before the event, pick your long run training to practice and follow your plan, or build up to it. As mentioned above, first try using the products that will be available on the course. If those do not agree with you, start experimenting with other products.
In the the days before the race you should make sure your fuel stores (muscle glycogen) are full. In the old days, extreme carbo-loading regimes were followed with days of no carbohydrate, days of extreme carbohydrate, a depletion run a week before, etc. This practice is not necessary. Very high muscle glycogen levels can be achieved by just eating more carbohydrates.
Eating more carbohydrate does not mean overeating or eating as much as possible! It just means making sure more of your daily calories are coming from carbohydrate at the cost of some fat. It is a good idea to have the last large meal at lunch time the day before and to have a lighter meal in the evening. This is also something you should practice in the weeks before or when you have a smaller race coming up. If you frequently suffer from gastro-intestinal problems, reduce your fiber intake to a minimum the day before the race.
From a purely practical point of view, you also need to plan in advance, especially if you are travelling. Make a reservation at a place where you know the food is good. Don't wait and make it up on the go and end up at fast food place or lining up for hours. Your legs need to work hard enough the next day.
A Helpful Checklist
Study the course, the nutrition on course and develop a plan. Practice practice practice: Train with your race nutrition plan, train with the drinks on course, train with gels or whatever you will use.
Practice your breakfast plan and also the meal plan the night before. Find out what works best for you.
Make a reservation for dinner the night before at a place that you know is good. Don't wait till the last moment.
Buy your race nutrition, don't wait till the last moment. Increase your carbohydrate intake by eating more carbohydrate rich (not just eating more). Reduce fiber intake 1 to 2 days before the event if you often suffer from gastrointestinal problems.
Have your standard race breakfast that you have trained with 2.5-4 hours before. Avoid high fiber, high fat and high protein foods. Aim for at least 100 grams of carbohydrate. Drink enough fluid and check that your urine color is light.
The Hour Before
Start your race fueling 5-15 min before the start (a gel with a few sips of water is an example).
During Your Marathon
Stick to your nutrition plan, but don't stick to it at all cost. Don't experiment with anything new. Stick to what you have practiced.
Aim for 30-60 grams per hour. Use sports drinks gels, chews, bars, depending on your personal preference. You can mix and match to achieve your carbohydrate goals.
Avoid high fiber fat and protein intake during the run. Don't overdrink, don't under drink. Try to match our sweat loss or a little less. Some weight loss at the end (2% of your body weight is fine).
Don't use excessive salt or electrolyte intake.