We took our son when he was 10 months old, and he did just great.
We made sure we had a good reclining stroller for him so he could nap comfortably when he was tired. I carried light blankets and clothespins so I could shield him better from the sun while lying down (the pins also worked great for holding the park maps on the open hood of the stroller!)
I carried 8oz. cans of ready-to-use formula for him. They required no refrigeration, so I could just toss them in the diaper bag and open/pour into a clean bottle when he was ready. I know others have used powder, and mixed with water when ready to feed, but I was concerned about how his system would handle 'foreign' water. Better safe than sorry.
I always made SURE that he ate when he was used to eating...every meal. Didn't matter where we were or what we were doing. If it was time for lunch, either DH or I would find a shady spot to feed him while the other continued touring with our then 3-year old, or everyone stopped to eat. Again, our son was very used to a pretty standard schedule and keeping to that kept him happy. That makes everyone happy.
We carried plenty of diapers, extra clothes, and even jammies if we knew we'd be touring late. Carried two washclothes and a travel-size baby bath for cleanups if we chose to put him in his jammies. (he'd get a bath in the morning) This way, he could be completely ready for bed the minute we hit the hotel room.