And... the only sensible option really said here is to save it. Anyone who is above 20 should have at least 500 dollars in their bank account for emergency funds, because life will fuck you up, one way or the other.
Barring that, if you're in school, I would invest in a good tablet, especially if your professor gives out online notes. Editing note pdf files without wasting paper, and having a centralised electronic place to keep it will make your life extremely easy. Buy one that comes with a pen, and has good sensitivity to it, because an iPad 2 will not suffice. Unless of course, you are an arts student and can type out everything on a laptop.
Also, looking classy goes a long way. With that 700 dollars, you could either invest in a 300 dollar coat, that'll keep you warm, and good looking, or go with a nice pair of boots/shoes. If you're lacking a suit, you could go for a decent one with half that.
Edit: Can we make it a rule that iDunno can only have one response per thread.