For any international trip there will be some important documents you will need to get and take with you. However, getting them together for a long trip isn't as much trouble as it may sound - you just need to give yourself time before the trip to acquire such things as your passport and possibly a visa for the country you are going to.
Your passport is one of the most important documents you will have while traveling and you should do everything you can to make sure it is safe. The passport certifies your identity and nationality and is the property of the government of your country. A passport is required to enter almost any foreign country and even to re-enter your own home country.
There are some countries that require a visa to allow you to travel into or through their country. A Visa is a stamp placed into your passport as proof that the countries government has allowed you to travel to and stay in their country. Visas are issued by embassies and consulates.
Health insurance is always a good idea even when you arent traveling. However general health insurance may not be adequate for a travelers needs and special travel insurance can be very expensive for longer trips (over a month).
The International Certificate of Vaccination (the "yellow health card") is the document for recording all of your travel immunizations. About the only thing this is currently used for is checking for Yellow Fever vaccination when coming from an infected areas such as sub-saharan Africa and the Amazonia regions. Very rarely some border guards may also check for a Cholera vaccination in some third world countries.
On September 19, 1949, the United Nations established the International Driving Permit to facilitate the travel of motorists in foreign countries where language barriers create difficulties for both motorists and police. This document establishes the right for a person to drive in another country. The International Driving Permit (IDP) must be accompanied by your valid state driver license. It is not valid in the country of issue.
Student cards and hostel membership cards can be used to save money - something I'm sure that everyone likes to do.
Your "important documents" should contain the following: Passport and Visa's, Yellow Card, Insurance Papers, any International Drivers license or other important official certificates, your ATM cards, bank cards and traveler checks. Also your Airline and travel tickets.