I like to run marathons in shorts, if at all possible. They are less likely to cause chaffing than tights, and the shorts I run in have handy pockets across the back for me to stash all my gels that I eat for nutrition in. Black shorts are perfect, because if it rains, they won't be too see-through.
I usually alternate between a few flavors of energy gels, starting at the 10 mile mark and eating one every 3 miles.
I try to time my running shoes so that I have a fairly new pair with less than 100 miles on them. This pair only has about 30 miles, so they will have good shock absorption over the miles. But they are the same trusty brand I always use, so I won't have to worry about breaking them in.
Luckily, I don't have to worry about a period for this marathon, but if I did, I'd be sure to pack Softcup. I am a recent convert, but I can say that this will absolutely be my running choice from here on out. It's period protection that can be worn for 12 hours and is completely comfortable. You don't even notice it's there, and it is made without latex, silicone, dioxins or anything creepy like BPA. Also, there are no strings or wings so you really just kind of forget about it. Once I put this to the test during a cycle, I was thinking this was truly one of the greatest inventions for women ever! It's also perfect for other sports like swimming, and can be worn overnight. As an added bonus, Instead Softcup is not associated with Toxis Shock Syndrome (TSS).
The other things I always pack are a peanut butter and jelly sandwich on whole wheat bread for breakfast the morning of the race, two ibuprofin (which I put in a teeny tiny plastic bag that spare buttons come in with shirts) to keep in my pocket during the race in case of injury (this I learned the hard way) and a tiny bit of vaseline for chaffing or chapped lips in case of windy conditions. Don't forget to bring your race registration, and write any pertinent health information on the back of your race bib just in case something goes wrong on race day.
Now that my training is done, I'm just hoping for good weather and a healthy morning the day of my race - and that I will be able to finish injury free.
Disclaimer: I was sent a month supply of Instead Softcup to try, and I was compensated for my review. The opinions stated above are my honest opinions and are not influenced in any way. If you would like to find out more about Instead Softcup (I recommend you do!) check them out on Facebook or Twitter.