To the nervous guy on the shuttle (and indeed, to any person nervous about giving a presentation in their field),
Breathe. Drink some tea. It’ll be ok. In a few hours, it’ll all be over.
And remember this: No one knows your stuff better than you do. No one, because you’re the one who did it, with your own grubyy little paws. If you’re a fifth year graduate student, you may very well know more about your project than your advisor. So do not worry, do not fret. Unless you meet a total jerk, no one is going to try and one-up you at your poster. They will ask you questions, sure. They might ask you stuff that you don’t know. But that’s ok! They want to make your mind and your project move in new directions. They don’t want to cut you down, and they certainly don’t want you to fail at your presentation!
So don’t feel bad, don’t stress. And above all, try very hard not to stay up ALL night before your presentation running it over and over (unless, of course, you really don’t know it). Be good little neuroscientists. We ALL know that a night without sleep doesn’t help your presentation, even if it was a night spent preparing. Sleep will help you far more.
So breathe, relax. Trust in yourself. You know your stuff, and you need to believe that you know it. So get a good night’s sleep, and go get ’em, neuroscientist!