You won't go far without it.
Unless you're going to a domestic destination, you'll need a valid passport. If you don't already have one, get one at least a couple of months in advance. Keep it securely on you while you travel, and lock it in your hotel room safe during your stay. It can be difficult to replace a lost passport, so avoid taking it with you during activities.
You may not intend to drive while you're traveling, but that doesn't mean the opportunity won't present itself. Having a driver's license is also useful in case someone asks to see some picture ID and your passport isn't handy. If you plan to drive, make sure your license is accepted in the country you're traveling to. You may need to arrange for an international license before your trip.
Always keep your laptop and your camera in your carry-on luggage. Also make sure to bring battery chargers for each and an extra memory card for your camera. You can keep the camera charger in your checked baggage to save room.
It's important to keep yourself entertained during long journeys. It's also the perfect time to catch up on reading. That said, restrict yourself to one book or one electronic system (for example, tablets, laptops) so your carry-on won't get too heavy.
It's difficult for most people to do this, but the key to packing sensibly is to plan what you're going to wear each day that you're gone. To save on space, try to stick to one jacket, and if possible, wear it during your journey. Shoes take up more space than clothing, so be brutally selective.
Always bring two swimwear items so that you'll always have at least one dry suit.
Some people are very particular about skincare, but remember that hotels always provide guests with in-room soaps, moisturizers and shampoo. If you can't do without your cream routine, try to purchase your favorite products in travel-size format and pack them into a small travel pouch to avoid spills. Pack these in your checked baggage since many airlines don't allow liquids in carry-ons. Don't forget your toothbrush and toothpaste!
When considering cosmetics, resist the urge to take the whole boudoir with you. Stick to what you need and try to coordinate your selections with the outfits you plan to wear. Where possible, pack these in your checked baggage, ideally in a travel pouch.
If you absolutely must bring jewelry but don't plan to wear it while you travel, keep it in your carry-on. Jewelry and other valuables run the risk of getting stolen if they're placed in checked baggage. Otherwise, bringing sunglasses is never a bad idea, but they're also easily purchased at any destination.
