Do you have one, and is it valid beyond six months of your proposed date of return? Make photocopies of it to take with you (or scan it and email it to yourself) and leave a copy with someone at home, in case anything should happen.
Visas:
Check out all the countries you want to visit, especially if you want to work, and make sure you know all the red tape. Apply for any visas way ahead of time, as some consulates can take several months to process the visa.
ISIC card:
This could be the best little piece of plastic you'll ever own. ISIC, the International Student Identity Card, has negotiated amazing discounts across the globe on car rental, shopping, museums and attractions, hotels, and much more. You'll also need to be a cardholder to get the fantastic deals on HighTime Travel airfares. Don't leave home without it!
Money:
Take an extra job, and do whatever you can to save like mad - you'll thank yourself when you have a bigger daily budget on the road. Start to set a budget for the following things: flights, travel and tours you'll be booking before you go, and your daily spending budget while you're on the road (which will depend on the countries you are traveling to). Allow yourself a portion of money to come back to, so you won't be entirely broke when you get home.
Keep in touch:
Don't forget to set up your email to keep in touch with your friends, family and co-travel addicts! You can also keep in touch with a global cell phone, allowing you to make calls from up to 110 countries. HighTime Travel has these on sale from $29. Or, use the ISIC low cost international calling card which gets you cheap calling rates as well as a handy toll-free voicemail number for family and friends to leave messages on.
