Lots of tips already!
For our second daughter, we did what many others have said on this thread.
We went to WDW when she was just over 2, and she was daytime trained (still wore a pull up at night, because I didn’t want to deal with random wet sheets).
We did use pull ups on the trip, including the flight there. I just didn’t want her to get stuck on a flight or in a line when she had to pee.
We also had the rule that if we went to the bathroom, everyone has to go. We actually used that on our most recent trip (kids were 4, 7, 9) too.
We always went before and after meal breaks.
We did have to leave one ride line if I recall, to make an emergency bathroom break. It was voyage of the little Mermaid, and the worst part, was trying to get back in line to meet up with the rest of our family.
ETA at 2-3, their bodies are so small, they also trigger the auto flush toilets randomly, which was scary. I would use a little piece of toilet paper (or my hand) to cover the sensor when they used the toilet.
Honestly, she did amazing, and there were zero accidents during our trip.