Have a little baggy with some advil and a tums or two in it. Lifesaver if needed. On one ride, I really wish I had had a blister bandaid (they have a really strong adhesive) to cover up a place that was chafing.

Bring a snack or two that you can reliably eat and save it until the last part of the ride. I needed fuel, but could not stand the thought of eating what they had at the rest stops by then end of the ride. Luckily, a bag of fritos saved me.

Same with drink. If you normally drink something other than gatorade, bring a baggy or two of the mix or tablets or whatever to give yourself a break from the gatorade if it starts to get old- or at least alternate gatorade and water. After my first century, I couldn't drink gatorade again for months.

Ride from rest stop to rest stop.