We just took our 3 yo with her car seat and a foldable wagon. You can check the car seat at the airport for free (which we did last year, advice is to shrink wrap it with shrink wrap from your local home improvement store for $8 and the roll travels with you for the way home), gate check or carry it on. This time we forgot to check it when we got to the airport so we gate checked it for our first flight then realized our daughter would be much more comfortable in her plane seat if she had her car seat so she used it in the flight. That is the way to go in my opinion because it kept her under control and she actually slept most of the flight. As for carting it around, it fit perfectly in the foldable wagon, (that we also gate checked for free) and she got to go around the airport and on and off the ship comfortably. Plus we had piece of mind with the crazy cab drivers. We didn’t do any excursions so no advice to give there as far as how well equipped the vehicles are to secure a seat. However, we did use the wagon to get around the ports we walked.