If you don't have specific medical problems, it's doubtful you need to do "anything special" in the days before the ride. The typical response to questions like this -- is to simply eat "normal food" in normal amounts.
New century riders are no more successful than old hands when trying something "new" for a ride. Just remember to snack while you ride and continue to "sip" water or sports-drinks throughout the ride.
No guzzling or gorging required, good luck.