A half dozen pairs of clean underwear.
Sufficient balance in cell phone..
Passport, visa, record of inoculations, travellers' checks or some kind of money/credit card acceptable in the country you're visiting
Not much. These days you can get from any point in the world to any other point in like 2 days max. So, I'm gonna say cash or card would be a good start. Just buy stuff as you go
Passport. Passport. And a passport. O_O