Answered by Narendra
For any international trip you will need a passport that is valid well beyond your travel dates, as many countries ask for several months of validity remaining on arrival. Checking your passport early is the single most useful thing you can do, because renewing one takes time you may not have close to departure.
Depending on where you are going, you may also need a visa, which can take anything from minutes online to several weeks through an embassy. The requirement depends on your nationality and your destination, so confirm it for your own passport rather than relying on what a friend did.
Beyond the passport and any visa, keep copies of your key documents somewhere separate from the originals, and carry the confirmation for your trip. Border officers and hotels occasionally ask to see proof of your onward plans, and having it ready saves a lot of stress.