are you riding by yourself or with a group? If you aren't going to be riding through any places where you could buy something make sure you bring more food/water than you think you will need. I went through one bottle of endurox, 5 gu's and a mountain dew code red on my first century. If I did one again, I would a little more often. Probably every 30-35 minutes instead of 45 minutes.
Replacing electrolytes is important also on a ride this long especially if you are doing all the work yourself. After the ride, you will probably crave something, go eat it.
Also... don't push too hard too early. The first 40 miles of my ride I felt like I was barely putting in any effort at ~18 mph, but your legs will start to feel it after a while. Miles 65-85 seemed to be the toughest for me, yours may vary.
Days leading up the ride, cut the volume a bit. Don't overthink it, just relax!