The oxygen masks of class ranking? Please reply!

We all know the feeling, but somehow it gets worse in senior year: That fateful day when people find out their class ranking. My senior class is pretty miniscule, so within half an hour we could guess at the entire list of rankings, and it shook our world up. The people closer to the top were envied, and the people bringing up the bottom of the list expressed their freak-outs in various ways. This madness begs a question: When it comes to helping your friends, how much is too much?

I try to accommodate any of my classmates that ask for my help, because I've been in situations where I have desperately needed a nudge in the right direction. One of my best friends, especially, knows he can always count on me for any help he needs. My teacher pointed out a very good way to look at this dilemma, though: "When you're in an airplane crash and there's no air and you're dying and you've already finished all your peanuts, what do you do?"

My friend summed it up: "You put on YOUR oxygen mask first, and THEN you help other people put on theirs."

So this question I put to you: Where do you draw the line between covering your behind and helping out a friend in need?