DS had an aide until this past year (he's in 8th grade). All drivers are now epi trained, and he rode three different buses each day (one to the high school with high school kids, one from high school to middle school after his first period there, and one home. We didn't do the activity bus this year but could have if needed.)
We had different accommodations as DS grew older: driver wiped down his special seat up front. Then that was excluding him from social situations, so he would pick up a wipe upon entering the bus and wipe down his own. In elem, the drivers still had assigned seating, so that helped.
It was just in our 504 because our district's Sped Dir put it there at the very beginning.
Along with eating cafeteria food (though we haven't done that).