I did my first century a month ago. I went solo and had a great time. I actually ended up doing 110, instead of 100.
I missed a turn at one point and headed off about a mile in the wrong direction before turning around. It really didn't effect me much, but it was a bit of a downer.
But, the thing is, through the ride I felt very good. It wasn't until I'd completed it, that I realized I'd extended myself a bit.
Since then, I've done several 60 milers, a couple of 70's and a couple of 80's without any real prelude. Just went for a longer ride.
But, here is what I did for the ride:
1. Took spare tubes.
2. Took two sandwiches, and two pieces of fruit.
3. Took gatorade instead of water or tea.
4. Took toilet paper.
5. Made sure I had spare CO2, my valve, an allen/screwdriver tool(mine is small, but works great). A leatherman multi tool.
6. A debit card.
7. A cell phone.
8. ID.
9. This was entirely unnecessary, but I took an extra pair of shorts and shirt. In the event of weather concerns, I'd consider taking something to protect against that.
CONCLUSION: I have a large Topeak bag on back, I took advantage of this. I felt as if I were preparing for the Odyssey and might have taken more than I needed. I did eat the food I took with, I didn't over eat before going. I finished feeling pretty strong....but as if I'd exerted myself. By this I mean, I wasn't starving to death, ready to fall down, or very hungry. But, in going down a flight of stairs, I could feel it in my legs pretty good.