Why, at the end of the movie when the team is burying Gerry, do they sing "Na Na Hey Hey Kiss Him Goodbye"? As I recall (and it has been a long while, so this might be a case of misremembering the movie, and I'll be glad if it is), the song has no specific relevance besides being on the soundtrack, which they obviously would not have known. And even if they had, why are they singing a song that amounts to being a kiss-off/taunt while they're burying their teammate and friend in the first place?
I've always thought the words to the song were "Na Na Na Na, Hey Hey Hey… Goodbye". Pretty sure they weren't using the song to taunt anyone. It was a way of saying goodbye to their friend. Also this is a song they all sing on the bus on the way home from camp.
It's a classic Ironic Echo, even if used as a taunt they are re-purposing the song (and slowing the beat down) to give it a somber, meaningful significance.
And they did use it earlier in the movie. Several times actually, always as a taunt. Watch the movie again, it comes off as a pretty epic moment.
So… How did Gerry die? He survived with crippled legs, yah, but then he just dies at the end. How? Did he pull a Star Wars and lose the will to live?
While a lot of crippled people can survive a very long life, being bedridden increases your chances of an infection or blood clots due to being unable to move around or fully take care of yourself. They did state he lived some ten years after the accident, so that would probably rule out any further complications stemming directly from the accident.
In Real Life, Gerry got into yet another car accident ten years after the events of the movie, as stated just before the end credits.
At one point we see Coach Boone vomit before a game. It isn't referenced before or afterwards. So what exactly was the point of it?
It was probably to highlight just how much stress/nerves he was under given the whole "lose one game and you're fired" situation.