How far is the drive? My GCC is a pretty good traveler, he comes with me when I visit my parents and it's a two and a half hour drive. It's not his favorite thing but he doesn't mind it. I know you can't control this but I've found that the weather makes a difference. He hates if we're driving in rain or if it's still kind of dark out when we leave. He's gotten used to the wipers going and he does better now but it's something I hadn't thought of before.
I'm not sure what kind of carrier you're using but that can make a difference as well. I put a lot of money into a wingabago carrier because I knew we'd be using it often. You want something he'll be comfortable in. My carrier came with a basic dowel perch, I vet wrapped half of it to give him the option. I found that he wanted to be up at the top of the carrier so I found a perch to put up there and that's where he spends most of the drive, he likes to be able to see out the windows. I took one of his cotton squid toys from his cage to put in his carrier and he likes to climb on it once in a while. You'll want to use soft/ light toys so they won't cause any harm if they swing into your bird.
Give him ALL the snacks lol I get the carrier set up where Ben can watch me. I make sure he sees me putting all of his favorite snacks into his bowl and I make a big deal about it to get him excited. He loves walnuts so I give him a walnut for a step up and he steps onto his carrier perch without any problems. He spends the first bit of the drive picking all of his snacks out and then he moves to his higher perch to hang out. I always offer water but he doesn't usually drink it while in the car. As long as it's not too far of a drive I wouldn't worry too much about them eating/ drinking. I'd always make food and water available for if they want it. The first time I took Ben out in the rain he regurgitated (not sure why) so I soaked a bit of ginger and chamomile in his water for the next drive and he loved it. If I ever stop at a drive through for food I make sure I get a special snack for him. We usually stop at McDonald's so I get apple slices for him and he loves it!
You have to figure out what your bird wants. Does he want to see out the window or is he calmer if he's covered? Does the weather affect his behavior? And find ways to cope with that. Are his perches comfortable and does he have options? Find out what kind of perch he prefers. Does having music on affect him one way or another? Basically just anything you can do to make sure he's comfortable and make him feel safe. Pick one of his favorite toys to put in the carrier for him to play with. Shower him with snacks. Make sure you talk to him every so often, I think it helps ease their fear. You want to make car rides fun for him. He may never like being in the car so all you can do is try to make him as comfortable and happy as possible.
It sounds like you're doing everything right, I hope any of this helps!
