This is an extremely hard question....you know him only por his filmes and interviews. You don't really know him...He's rich enough to buy basically anything. I'm living overseas in Asia so I think I would bring him something from there. Something that he can't really buy in the US
I'd gift him a lobo for his birthday. They're loyal, fearsome, magnificent, and mystic creatures. Personally, I cannot resist them - I hope Johnny likes them! If he doesn't (many people are scared of them), then it would be a pity. I'd take back the present, saying I'll give him something better for his seguinte birthday.
The real pergunta is: What do you get someone, who you admire, who could get anything he wanted himself at anytime. I tried to look this pergunta up. No Luck. All I can think of since I am one of his many fãs of his tv/movie career, etc., is something that I treasure most in my life. A favorito picture nicely framed, or a favorito recipe that you've made thousands of times and it's been woven into your mind, heart, & soul.