Wow, 20 hours is a long flight. I'd hate to be on a plane that long, I can't imagine how boring it will be for Mascot!
I agree with what Crystal said above. I would put him in a larger crate so he has plenty of room. Put pee pads down for him to potty on. (Does he know what these are?) The water bottle idea is good too, but you should let him practice drinking from this at home beforehand so he knows how to use it. Also, give him a few toys to play with and nice comfy blankets to lay on. You also might want to put something in there that smells like you (like a dirty t-shirt) so he has that little bit of added security that you are there with him. Good luck!