I've only done one full marathon, so I'm not sure I have any great advice. You've done the training, and trust yourself and your body. You can definitely do this.
My race day routine is to have an energy bar, a bottle of Gatorade, and a cup of coffee in the morning. I like to get to the start area early, like 45 minutes before so I can use a portapotty. I don't like to feel rushed. I won't say that's ideal for everyone, but it's what I do.