Be Early and Be Prepared
My race partner and I were scheduled to be on the 8:15 Staten Island Ferry leaving from White Hall Station. We arrived around 8, and that was way too late. The station was jam packed, and we weren't able to get on to the ferry until 9.
Many parts of the city are in a gridlock during the marathon, so it leaves subway as your most efficient form of transit. Bring a MetroCard, and be prepared for subway delays too.
A lot of runners like to use GU or other energy gels during the race. I tried them for the first time, and it definitely gave me some extra energy.
[photo via @nytimes]