Depending on where you are going:
Passport, sunglasses, hygiene products, toiletries, at least a week of clothing, camera, laptop to stay in touch, power adapter, cell phone, charger, iPod or mp3 player and various shoes for each type of outing you'll be doing while there. Also make sure your credit cards will work overseas and bring a few hundred dollars in cash to travel with.
Last, make sure you know about visa requirements and immigration issues for the country you are traveling to. Have fun.