On our October trip, DS was 2 1/2. We were waiting to make the potty-training push til after vacation. He was #2 trained from just after age 2 and we did nakey-butt at home for #1, but he was no where near trained for out of the house.
In the car on the way to the airport he said, I have to go pee. Obviously there was no where to stop on the interstate and we told him. We get to the airport, check in and get through security and he says, I have to go pee. I take him in the bathroom, and he is completely dry (at this point it has been 3+ hours since we left home). He said, I don't pee in my diaper anymore. The entire week he told us every time and only had 1 accident. We did use pull ups the entire time. He has been completely trained since.
It was a bit of a pain to remember to take him before EVERY ride, show, fireworks, bus ride, etc. Sometimes we did forget and then would do the mad dash to the bathroom. Once, we stopped to see Peter Pan, and he was talking to him and all of a sudden my DS is doing the Potty Dance and told Peter he had too pee. Too cute. We were right outside the bathrooms at POC, so when we came back out Peter made a huge deal out of it. It was really cute.
It was a bit shocking since we were not expecting it and didn't even pack any underwear for him and just barely enough pullups. But it turned out fine and I always say boy Disney is magical, it even potty trained my kid!