Travelling out of the country is totally different from the usual out of town trips. Aside from packing necessary things, there is a need to carry along travel documents.
For countries that require visit visa or similar documents, it should be secured days before the booked flight. These documents will be checked thoroughly by the immigration officers who are based in each of the respective airports.
This will serve as your right to travel in their country in a given number days or length of stay.
Next to visa would be your passport. This would be the most reliable identification that you could carry when you travel out of the country. This will note all the entries and exits that you had in your previous travels.
Last but not least would be your identification cards. A driver’s license or social security card will as long as it is a government issued card containing your signature, photo, date of birth and address.