Some autistic are so withdrawn that normal toys won't work. High functioning means fairly normal, but has quirks like severe sensitivity to loud sounds, or very OCD. I have a friend who is autistic, but is a board-certified doctor, but has severe OCD. Sounds like this person is on the higher side of normal, so something to occupy his hands and mind like Kyle suggested sounds more appropriate.
I understand what you are getting at, but with all due respect, it's harder to quantify this (for lack of better terminology) at his age. That's because there is a wide range of normal and it also varies greatly where the child is on that autistic spectrum.
He's 5. If he is at age level, then all things that might be interesting to a 5 year old will apply. Thing1 was/is not on the autistic spectrum, but had developmental delays at that age. He also had a tendency to perseverate or hyperfocus on certain things, but I found that (when he was 5, which was in 1996) a lot of electronic learning toys (made by V-Tech, back then) were beneficial to him, as they were very interactive. Now, you have SO many more electronic devices that are available. He LOVED music.
As mentioned above, Legos and other manipulative toys are really good, as they teach much more than just building and making items, and they are good for fine motor skills, etc.
Like Vrai said - more information is needed. What are his interests? Does he like certain sports, or certain movie characters? Does he like music? If he is non-verbal, then maybe some type of interactive electronic device, which would even increase his verbal skills, or communicaion skills in some way, as well.