I'd ask his family in advance what his favorite things are, and be prepared with them. My oldest child (okay he's a man now!) is high functioning autistic, and I have a half brother who is also autistic - both enjoyed alone time with their favorite toys, and talking about their favorite subject a LOT.. over and over and over and over and over and over.
I don't think that any two autistic children are necessarily alike in what they like. Probably sensory toys are helpful, but you can't count on anything. And if they don't care for what you've provided for them to play with or do, don't expect to change their minds with a little coaxing!
Just be patient and loving, and prepared to be frustrated until you figure the guy out!