I just did my first century last saturday with a pal. I had a wrench on me to flip to my freewheel if I got beat, but ended up staying fixed the whole time. We rode like 4 miles then stopped to stretch. Otherwise we had plenty of water and an apple on the bike before stopping at about the 50 mile mark for lunch/to rest by a river. We were exhausted after, but it was super fun.

So not to underestimate the importance of food and such, but I don't think you need to stress about gels and all this other dietary advice. I don't think I'm in great shape, but I do ride at least 15 miles everyday (work and back), most often more for funzies/fitness.

Oh, definitely don't do a martini after =). I rested a bit after the ride then went to a gallery opening. We went for drinks after and one martini hit me like whoa. I was ready to take on world =).