The second main factor was nutrition and hydration. This isn't a slam dunk guarantee but it worked for me during this race.
The week before the race I started increasing my grains to about 10 a day. I chose whole grains and whole wheat (don't confuse wheat with whole wheat or multi-grain with whole grain) over white breads and pasta when possible. I try and select whole grains during the whole marathon training season and not just during taper.
The morning of the race the first thing I did upon waking was drink a full cup of water. I actually do this every morning and drink a glass of water before each snack and meal. I'm not a big breakfast eater before my long runs but knew before the race eating was important. I ate one Fall Harvest Muffin (recipe here) shortly after getting up and a second one 2 hours before the race start. I was still hungry and could have easily eaten another one but held off. I didn't want to be running on a full stomach.
My plan was to eat a GU (orange burst with caffeine) at miles 5,10,15 and 20. I didn't however, take into account the water stops were every two miles. I revised my plan to take the GU starting at mile 6, 10, 16 and 22. As it turned out I was able to take one at 15 and 20 anyway. Rather than run the risk of taking in a GU and not having enough water to wash it down, I would start the GU about 1/8th of a mile before the water stop.
Each water stop I took water until mile 10 then upped it to two cups. I needed to make sure that I was getting enough water and since I often wore half the water in the cup anyways, I needed to get two cups. The poor volunteers handing me water frequently got splashed too. Sorry! Water is always my beverage of choice but I changed it up and started taking Gatorade the last couple miles. I did this for a couple reasons. One, because I had the last GU at 20 and was still worried of hitting the wall and not having any GU left since I only brought 4 GU and ate 4 GU. Second, at my first marathon I remember being so tired towards the end but not wanting to take any more water or any more GU. I thought if I had Gatorade that it would help me. The only problem with Gatorade is it is sticky and spilling on myself is easy to do.
I was able to finish, almost sprint in and had plenty of energy. Next time I will repeat the same carb loading nutrition along with hydration that I did for this marathon.