I've gotten much better at this, through experience.
One of NJ Transit's Trains in action
Anyway, it seems like New Jersey Transit does this at least once a year - they are having a "STUDENTS RIDE FREE" week. Anywhere NJ Transit goes, you can go for free, by going to their Web site and filling out a form. I'm on their e-mail list, so I get reminders when this goes in to effect and I try to mention this to my classes.
Even if you are paying normally for public transportation - if you fill out this form and bring your student ID, it's a free week.
This is valid from 9/15 (Monday) through 9/21 (Sunday) and on all bus, rail, and light rails run by NJ Transit. They've also got a trip planner on the Web site, in case you're wondering "how do I get to NYC from where I am?".
Also thanks to Sue for a reminder on this one.
Web Site Link:
NJTransit.com - Students Ride Free!