Ok here is what I have thus far from your comments. Ideas that have popped up for the article.

Bring something familiar, a toy, crayons something that calms the child.

Explain at the time of making the appointment about the child's ASD and sensory issues so they can be prepared to either get the child in with no wait, or dedicate more time with him/her. 

The bad habits of bribes are worth getting through the ordeal the first few times. The kid will learn not to fear the appointment and not need these things after awhile.

Visual books are always a good idea, if possible take a few pictures (with the permission of the doctors of course) before taking the child in. Or take pictures while there if this will be a reoccuring appointment. Otherwise try to find other pictures to use as a PEC type book for visuals.

My son loved going to the eye doctor - I think he liked the darkened rooms and the glow off the various pieces of equipment.  Getting him to leave - now that was the problem! 

I'm sure his therapy experiences (see one of my comments to another post) would have been even more productive if the therapist came to our home.  It seems to me that sensory things the therapist might bring into the home would be easier to spot than trying to sort out all the sensory issues in each strange environment.

My son had many sensory issues (and he couldn't tell us what they were until he learned to communicate - so he would tantrum).  Actually, sensory issues were at the root of most of his tantrums - either directly or by being a reason he wanted to avoid doing something we wanted him to do.  He would only occasionally because he wanted something that he couldn't have.

As a result, doctors' offices were very hit and miss for a lot of years until he could identify to us the various smells (mostly), colours, sounds, plants, etc. that were objectionable to him.  Over time, he also began to understand that sometimes things like smells in the environment were really beyond anyone's control and he learned to just "grin through it" for a little while.  So if you see a young man sitting in a doctor's office with a forced grin on his face - that's my boy!  (it's also one of the "looks" that became a signal for an urge to tantrum coming on.)

Perhaps surprisingly he likes most doctors now, although he still doesn't really like the smell of many of the disinfectants and cleansers used in their offices.  He also hated whenever I really cleaned the house.  Fresh paint was also bad.

Uhg, I don't know if I have any helpful advice...but the last time I took Wyatt to a doctor--a dermatologist--I called them ahead of time and explained that if they made us wait in the lobby for an hour (they always do) that my autistic child might get loud and disruptive.  Their response was that I would be welcome to go outside.  Yeah, how thoughtful of them. 

Fortunately, there was a basket of crayons and a coloring book in the lobby. I also brought a bag of potato chips (highly reinforcing) and I didn't worry about whatever mess we made.  When our names were called, I selfishly took the crayons and book into the examination room with us even though there were other kids in the lobby.  We had a bad moment when Wyatt went screaming down the hallway back into the lobby.   Unfortunately, he bumped his head on the corner of a wall when he intentionally went to head bang. I hate to admit that I had to literally drag him away a few feet by his ankles.  I think he was simply afraid of a new situation.

But once we got into the exam room I let him climb on all the furniture and hang out on the floor, even though I wouldn't have permitted a typical child to do so.  Whatever made him comfortable.  After the exam (no probing in the ear or needles, fortunately), the receptionist gave him stickers.

We haven't gone to the doctor very much at all.  But, in the future, I think I am going to use a visual schedule that shows a lobby, a coloring book and crayons, a smiling doctor, and Wyatt getting a balloon or some other reward (McDonalds?) after the doctor's visit.