Our kids did not decorate their graduation caps, it just wasn't something that was done back then. I'm not sure if kids wanted to and weren't allowed or if they just weren't interested in doing it.
Our grandson's graduation was last month, and many in his class did decorate their caps. He put the Marine insignia on his as he was going to be leaving soon for training.
I don't understand schools that are so strict as to not let them decorate their caps.
I've never been to a graduation ceremony where they toss around beach balls, but I think it would be fun and something the entire audience could get into.

Why be so stuffy?
Times change. Boys (at least around here) don't wear dress pants and starched shirts and ties, and girls don't wear dresses with heels and white gloves anymore. Let them have fun at their graduation!! The whole ceremony doesn't need to be so solemn.