I just my first century ride yesterday and learned a few things. One is eat a good dinner the night before and drink a lot of water the morning of the ride. Take supplements like B vitamins, potassium and bring along some snack food and gels. I would also buy some anti leg cramps pills just in case you get cramps.
A well stocked saddle bag will help for any trouble you might encounter. I was lucky, no issues but my body did threaten cramps at 85 miles into a 117 mile ride w/ 5,600 ft of elevation climb. Stop and take a 5 minute break 2-3 times and stretch you less and body, walk around but hydrate and pace yourself.
Good luck, have a great ride!