Unless the school specifically writes in something different, it should apply to any/all school district activity.
For example: My son has a 504 plan in place for school activities but he is officially homeschooled through our Home & Hospital Instruction Program (HHIP). When he has to go in for testing (as required by our state law) their are bound by the 504 Plan. Today was one of those days when he was going in for a 3 hour test. When he showed up with his cooler of food (bigger than a lunchbox cooler, smaller than a picnic cooler) filled with snacks and drinks initially the test coordinator said he couldn't have the food in the room. To which my sister quickly responded, "Yes he can, he has a 504 in place that you're bound by. Also, incase you are not aware he can also...." then she went through the list and ended with "and you WON'T stress him out about it. Any questions?" (heh, heh... gotta love an family advocate! We call her the "other mother"!
He can participate in sports, clubs, school dances, etc., if he so choses and if our doctor supports extra activities (which he does). What was really important was to differentiate between the fact that he can do "extra" stuff but cannot do all day school - too much stress, too many missed days. IF he missed a dance, a practice, a game, a meeting - it doesn't affect his schooling - hence the difference.
Having said all that, doesn't mean they wouldn't try to fight you. As I mentioned earlier if you hit a wall, I would recommend finding out who the parent advocates are in your school district. One of the first individuals who was HUGE in helping me out has a son who has Down Syndrome. She's been fighting for his educational rights since he was a toddler and already knew everyone I needed to talk to about my issues. Rarely will school administrators or educators help - not because they don't care, but because they can't. The older the kids get in school the more distant administrators become (just from my experience), as they are dealing more with troubled students, not students in trouble.
Good luck!