One of the best ways to maximise your race on marathon day is to lessen the chances of hitting the wall or finishing poorly. The best way of doing this is to carb load before the event. This is only effective for endurance events lasting longer than 90 minutes as it takes this long before our muscles will be depleted of glycogen.
By carb loading, we effectively store extra glycogen in our muscles, that we can tap into when our stores are used up. The greater the amount of stored muscle glycogen, the greater the endurance potential of the body.
There are a few different ways of carb loading but for now we will look at the most popular and easiest way on the body. Assuming that we would start to taper at least 2 weeks before your race, we would not need to eat as much as we don't have as many calories to burn off.
It would look something like this, assuming we are running on a Sunday, have almost no carbs on the previous Wednesday and Thursday. This depletes the body of its glycogen stores. On the Friday and Saturday before the race, eat as many carbs as you can. A good rule of thumb is 4-5 grams (2-3 grams be normal) per pound of your weight. The body will not be happy about the loss of glycogen at first and will maximise its store afterwards.
This can double the amount of glycogen stores in the muscles and make the end of your marathon a memorable experience.
Good luck and enjoy your marathon. Remember ONE STEP AT A TIME!