If you're planning to take a trip, there are some all student travelers should make sure to have in their backpack.
Student ID card: You never know when it will come in handy. Save on museums, hostels in Central London, show tickets and sometimes even food! Always, always ask if a student discount is offered. It might not always be clearly advertised. Sometimes, it might only be $.50 but you'd be amazed at how much that adds up over the course of a trip!
Calling Card: Calling collect sucks and is very, very expensive. Drop a few dollars and give your parents a ring every once and awhile to tell them you're alive - or at least thank them if they've wired you some spending cash.
Good Book: Just like the ID card, you never know when you're going to want one. A quick trip to the embassy could turn into a five hour wait, or you might be locked out of your Seattle hostel from 12-2 p.m. with nowhere to go. A good book can make the difference between pleasurable passing of time and horrible, horrible tedium.
Journal: You may think that you are going to remember every single detail of your trip for the rest of your life but the truth is - you won't. Memories will fade, details will become fuzzy and after a few years, you might not be able to recall very much other than "I had a good time." Invest in a good, durable and journal and USE IT! Flights or train rides are excellent times to keep your book up to date on your adventures.