For airports, get special assistance. Be sure to explain exactly what you need. Most want to seat us first and have us wait at the front of a queue. This is too much for my dc, too many people surrounding them and pressure to transition. t's better for us if we wait behind and are last to board and depart from the plane. If you haven't already have sunflower lanyards at the ready. Many airports now have a sunflower lounge, it's quiet and much more pleasant for people/DC with sen. Just know that unfortunately most don't have departure screens so someone will have to routinely check on that in the main area.
As for destination, do you require any specific dietary requirements? Look for places where you can access foods the child will eat. If your DC has sensory issues with food and a severely limited diet you can get a drs note for baggage allowance to transport. Obviously usual restrictions apply.
Personally I would always go self catering and housed over a hotel. It's easier to create a routine and make things familiar for the dc. It does mean same shit different place but hopefully in better weather. Also means more time for shut downs and a larger safe space within many transitions. We do take bedding with us to make things more familiar at night times and follow the usual structure of our days.
For preparing, the usual shows, social stories, play therapy, books. Maybe visuals and a now and then for travel if you use them. Comfort objects and sensory toys/aids. Keep clothing, toys and any media for travel usual.
...I'm tired but might be back with more suggestions other people have already mentioned. We travel each year to our home country and it's been a learning process of how to make it work, 8 years in we are almost there 😅