Most centuries are pretty well supported in terms of feed stops. A couple of extra bars or gel packets as insurance is a good idea, as is two full sized bottles but you shouldn't need to carry food for the entire day.
For folks doing their first century I always give the same advice. Be careful not to get caught up in the excitement of the start and forget to pace yourself and don't rest too long at the breaks. A lot of folks go out too hard and fade which is easy to avoid if you just tune into your own best pace. FWIW I've done several with slower friends and find it almost as hard to ride much below my ideal pace as it means a lot more time in the saddle. The other big mistake is taking 30 to 40 minute breaks and having to warm up all over again once you get going. I try to keep breaks to just a few minutes to use the facilities, fill up bottles, eat a bit and restuff my pockets with food. I've seen folks sound asleep at rest stops and have to wonder how they ever got going again.
Good luck and remember to have fun
-Dave