I think the most important thing is THE passport, because you CAN'T GET PAST have to pass the security WITHOUT IT!. And The second important thing is money CASH, TRAVELER'S CHECKS and/OR credit cards. AFTER ALL, Because you REQUIRE FUNDS have to LIVE ON IF YOU EXPECT TO HAVE A GREAT TIME.  BESIDES, IN THE EVENT YOU MISPLACE OR when you lose SOME OR ALL OF YOUR the belongings YOU'LL OBVIOUSLY NEED MONEY TO SURVIVE . And The third important thing is TO HAVE VITAL CONTACT the information SUCH AS about the phone numberS for ANY the emergency situation like YOUR embassy, family, FRIENDS, OR THE LOCAL POLICE. or any helpers in your country. OF COURSE CLOTHES TO SUIT VARIOUS OCCASIONS WOULD BE CRUCIAL, ESPECIALLY IF FOR EXAMPLE YOU'RE ON A BUSINESS TRIP, OR WOULD LIKE TO WIND DOWN AT THE END OF THE DAY WITH A SPECIAL FRIEND AT A NIGHT CLUB OR RESTAURANT.  Now you can choose any other things that enrich your travel. You can pack servaral clothes on your taste. and You can bring any enjoyable devices such as A PAIR OF binocularS, mp3 player, AND/OR AN E-book reader. SO have a nice trip!  I'M expecting see you again at the airport in alive and in one piece!:).