Absolutely wonderful suggestions. As a parent of one serious/anxious child and one flighty/anxious child, I can sympathize. Just so happens, I'm also a child psychologist
One thing that I use for clients as well as my own kids is a modified form of systematic desensitization, a cognitive therapy technique. Have your child get comfy in a chair or on the bed, close his/her eyes, and take a few deep breaths. Explain that you are going to practice relaxing all the muscles of the body until they feel "loose, warm, and heavy like cooked spaghetti noodles". Explain that the brain sends signals to the body to tighten the muscles and make our breathing light when we are scared and that by breathing deeply and keeping the muscles loose, warm and heavy, we send a signal back to the brain that there is nothing to be afraid of. The images of heaviness and warmth are essential because they instinctively induce relaxation. When the child is relaxed and calm, begin to talk about aspects of the trip. Begin with reassuring images of holding hands with Mom/Dad, looking at pretty flowers, riding somethig easy like the train. Remind the child to keep those muscles "loose, warm, and heavy". Then slowly begin to add more challenge to the images, talk about riding a new ride, about the feeling of minor turbulence on a plane, about any mildly scary thing that child has worried about. Once again remind the child to stay "loose, warm, and heavy". Have the child express the things they are worried about while concentrating on spaghetti arms and legs at the same time. If he/she becomes tense, remind him/her that these are just words, he/she is safe and comfy and just practicing thinking about things in a new way while staying relaxed. Ask him/her to notice how different it feels to think about scary things when the muscles are loose. It makes us feel braver to stay relaxed while thinking about worrisome things and then we can think of solutions more easily. Have him visualize carrying out those solutions while staying relaxed.
When you get to the point that the child has experienced getting a little anxious and calming himself by relaxing, then stop for the day and praise him. Another day you can start from close to that point and gently take on some slightly more anxiety provoking images while practicing staying "loose, warm, and heavy".
It takes 4-6 practice sessions for most children to master this but it is very powerful once they "get it" and can begin to use it to self-soothe their anxieties with less coaching from you. Remember to praise and tell them how proud you are of them for learning how to use their body to comfort their worried brain.