First, I just noticed another post of yours re different brands of generics and effectiveness. I've noticed a difference, too, and your pharmacy will order the brand you prefer. You'll have to double check when you pick the prescription up to make sure it's correct, but it's worth the extra trouble.
Re this topic, we tried homeopathic things first (like Rescue Remedy) with no success. Valium worked best.
Also, it might seem obvious, but try to smooth the way as much as you can for him with the different employees and prepare him for situations he'll encounter. I don't know how much stranger anxiety your son might have, or how strict and busy your airport is, but some employees can be hugely stress inducing even for a jaded adult traveler!
We fly a lot, and fortunately we have a small airport so the security employees don't feel the need to bark at people like they sometimes do at some hubs where they're overwhelmed. We DO very occasionally encounter unpleasant flight attendants, though. Talk to the gate employee and explain there's a medical situation so you can preboard, get him settled into a window seat if it's possible, make sure you have a favorite snack for him and get a drink when you're through security, bring along some noise-cancelling headphones and a small blanket, etc.
Good luck!