You could look into noise canceling headphones or bring along an item that you know will help him calm down. Also if you take him to an amusement park call ahead and talk with guest relations. Most amusement parks that I have taken my son to have an "Autism Pass" which allows you to enter rides through the exit to avoid being in large groups of people.

Another comment about the noise-canceling headphones...my son (5 yrs old) does not like hats, sunglasses, anything on his head. We got him child-size, lightweight noise-canceling headphones. At first he didn't want to wear them, but once he realized they HELP him he wears them happily. We started giving them to him when my husband mows the lawn so it was something he could get used to at home. The headphones allow him to hang out with Dad, but also feel safe. Last week we went to an event - motorcycle racing - and my son kept the headphones on the whole time, even when the bikes weren't racing, because the announcer over the speakers was too much for him. He ended up have a wonderful time and was so into the races my husband and I were absolutely shocked! I truly believe without the noise-canceling headphones he would have been jumping around, hitting, complaining, wanting to go home, etc. We always hesitate on bringing him anywhere loud because of his behavior, but now we're going to try more things and bring those bad-boys with us everywhere just in case he needs them!

Some parents are naturally over-protective about their children. My son does the same thing from time to time. I always immediately sternly tell him "No! Nice hands, no hitting!" That's his cue to stop LOL. Immediately after I redirect/correct him, I always turn to the parent(s) and say "I'm sorry, he is autistic and we are working very hard on his behavior, I'm so sorry (again)." ((which is the God honest truth))... Usually that backs the other parent(s) down, but once a lady did go off, but she looked like the jerk in front of everyone including her child who was embarrassed of her actions and even begged her to stop and that he was really okay and it really didn't hurt. She ended up apologizing to me for her verbiage. Sadly, the other parents gathered their children away from her son at the playground the remainder of their time there.

GO to guest services and ask for a disability pass...Most amusement parks have some type that allow waiting in a different area, shorter boarding, alternative entrances and exits...headphones with music is a good idea for redirection/calming. Also ask them about an quiet calm spaces that are available and mark them on your map..often in the first aid stations, but not always. token boards can be extremely helpful (you can get token systems on your smart phone if you have one) Pecs.com also even has a "Waiting for" app that may be helpful.
Goodluck

Sorry, as for over-stimulation. My son also goes through that and he also will have a meltdown if you put anything at all on his head (hats, earphones, etc).,He is non-verbal for the most part, just learning to use some baby words (he is 8)... We usually take him "for a walk" away from the crowd/noise somewhere semi secluded until he refocuses.