The first thing I'll describe is transitions.
MJ could not handle any change from routine or schedule.
At school, there is in day and then outside day for recess every other day during the winter. One day when I picked MJ up from school he was so emotionally upset rambling about how the kids wanted to have in day instead of out day and now the whole week was going to be off and how horrible that was and the world was going to end.
When I pick MJ up from school, I MUST drive STRAIGHT home. Any detours, or errands, or different routes are just too much. He will freak out. Even if we're going to go somewhere fun, it doesn't matter. He can't handle it. Like I know he loves going to the library, but if I get him from school and say we're going there BEFORE home, then he won't do it. I always joke that one day I'll pick him up and say we're going to Disneyland and he won't want to go.
Now, all these things aren't terribly hard to deal with. The teachers at church learned that they need to tell us ahead of time when they are going to rearrange the chairs or skip class. And I knew I had to tell MJ the daily schedule in detail especially if it entailed anything different. Yes, sometimes I needed to take a detour after school or change things around, and I still did them. MJ would have his little freak out, but I could deal with it. I didn't think it was that big a deal, but this was just one of the things I learned MJ freaked out a little more than your average kid.