I was wondering about his age. I know that can make a huge difference as to what types of things you try.

Sometimes ear plugs help me, and sometimes they make things worse. Since you don't want to use ear buds for him, that might be an option. It really depends on what he's most sensitive to.

I would avoid having a wide variety of toys, simply because that is probably overstimulating him. If he has too many "options," he's likely to get into overload.

Probably not a good thing, but I often have to sleep through longer trips, especially if I'm not driving. I usually take a Benedryl. I know that's not an ideal method, but if you have a long family trip (although, honestly, if I were in your position, I'd avoid that for now), you might need to, for his sanity.