In addition to many fine posts, suggest eating good meal night before as the body takes many hours to digest food.
Also start increasing water you drink the day before the race. And drink healthy amount of water upon getting up on ride day.
Also like the concept of going easier for the first hour+. Our bodies seem to like it more when we start with a controlled ride as it allows us to maintain or increase our pace over the rest of they day instead of wiping us out.
And of course comfortable shoes, bib, chamois cream and gel gloves to cushion the bumps. But your probably know all that already.