2. Vitamins - Get on some kind of regimen and stick with it. Even if you don't regularly take vitamins on a daily basis, do it on your trip. Take extra vitamin C, zinc, echinacea, Airborne, or something equivalent and start it a day or two before the trip and continue it after the trip. On a couple of vacations, I got sick the day after I got home, probably from the sick person I was seated next to on the plane ride home.
3. The pink stuff & antacids - I think the liquid is too cumbersome especially with the liquid nazis at security these days, so get the chewable tablets. If you are going to a place where the food is very different from what you are used to, you might have some stomach issues or what my grandma calls "oily stomach." The good thing about the chewable tablets is that you can use them as a preventative measure by chewing one before you eat and it will coat your stomach. I chewed on these things like they were going out of style when I went to China because the food is so oily and I never had any stomach problems. I don't like to take pills and medicines that just mask symptoms, but I don't want to have stomach issues in a foreign country either. You will be thankful you brought antacids and so will your travel partners. If you are like me all airplane food instantly turns into enough natural gas to power a 777 at least a few hundred miles. At the Dubai International airport there was a pharmacy and I bought some tablets called antacid/anti-flatulence and they are amazing. They really help when you eat something like a really strong curry and your stomach is just gurgling out of control.
4. Important numbers list - In your wallet or somewhere safe, put a list of your credit card numbers and the company phone numbers in case they get stolen or lost. On this list you can also include contact numbers and website logins and account numbers. You never know when you'll need to access things. The good news is that in just about every country except our, internet access is ubiquitous and free. If you rely solely on your smart phone or website backups, you might not be able to access those as freely as you think, especially if your phone gets lost or wet, or you happen to be in a country where their fire wall blocks certain cites (i.e. China, Vietnam). Also include your passport number, expiration, and any visa numbers too. You should also have a photo copy of your passport with you too. I made a file on google docs with all of this stuff and when I was in China, I couldn't access google docs for whatever reason. I did need something from that list and I was glad I had it in my passport wallet. If you are worried about having a list of these things with you, then disguise some of the numbers and passwords.
5. Outlet adapters & Chargers- Obviously if you travel with electronic devices, this is important. Just about all electronics will convert voltage, so you won't need a converter. But you will need an outlet adapter so you can plug it into the wall. Many hotels have universal outlets in the rooms, but they might only be on the desk and there might only be one. If you have several devices to plug in, then this won't help you. So bring adapters. Chargers are only necessary if you have a device that requires them like a camera, iphone, or laptop. This also includes battery chargers. On a recent trip to Thailand I brought 2 sets of camera batteries, but they both drained before the trip was over. I didn't bring the battery charger because I thought I had enough juice. I didn't really want to buy more lithium whatever-the-hell batteries so I had to be selective about using my camera.
6. Change of clothes and some toiletries in carryon - I don't always do this, but it's a good idea because you never know if your bags will get there or not. My partner has the philosophy that the bags will not arrive, that way we are pleasantly surprised when they do. On a trip to Nice, France my bag didn't make the connection in Paris and I was without anything for an entire day. It was terrible not having a change of clothes after I arrived and took a shower. I always look forward to that shower after I arrive to make me feel human again. So, at the very least put an extra pair of undies and a long-sleeve shirt in your bag because planes can get cold.
7. Printout of reservations - I know that this is not a very green practice, but you can always print it on the back of another sheet of paper that you already used from another trip. Make sure you recycle the paper afterwards. Even though everything is electronically based these days, if they can't find your reservation and you have nothing to show them, you might be S.O.L. Or it might take a long time for them to search for it. This happened to me in Phuket, Thailand and Kuala Lumpur, Malaysia when I checked-in for my flight. Malaysian Airlines couldn't find the ticket number because my ticket had been reissued by Delta each time there was a schedule change. So it was Delta's fault but I was flying with Malaysian and there is no Delta office in KL and I didn't have that print out with the ticket numbers. I just had the itinerary printed out. They told me to go to the ticket office down the way and have them find it. All I had was the boarding pass stub from the previous flight and the record locator. Fast forward 20-25 minutes and they found it. But that time could make the difference in making your flight or not.
8. Frequent flyer cards - Don't travel with all of them, but in the event you get bumped to another airline or some other kind of cancelation incident, you will still get miles, preferred seats, or even better treatment because you are a member. See previous post on this issue. If you are moved to another airline, it is much easier for them to add your number right then and there than it is to retroactively request credit after the flight. Also, in the event you have a cancelation or some other mishap, you do have a choice in airlines. If you know that an alliance partner airline can get you to your destination vs. the one they are telling you is the option, then ask for it. Don't assume that the airline agent knows everything about all possible airlines. I have airlines' numbers programmed into my phone and if you don't, the number will be on your card. One time I was on the plane from Minneapolis to LAX and they canceled the flight due to a mechanical issue. They made everyone get off the plane and get in line to rebook. Instead of getting in line, I called the airline and told them the situation. After a few minutes they had me confirmed on another airline's flight through Salt Lake City and back home. All I had to do was walk to the new flight's gate and pick up my boarding passes. All 200 of the other poor schmucks were waiting in line while I calmly made my way to my new flight.
9. Ear plugs - These might be useful on the plane and depending on the airline and your destination, they might provide you with some in an amenity kit. Don't throw those out. When you get to your hotel, you have no idea what kind of noises you will encounter or how thin the walls are. You could be woken up in the middle of the night or extremely early by anything and everything. In St. Maarten it was frogs that sounded like birds. In Phuket it was peacocks. In Las Vegas it was the whirlpool tub in the room above and housekeeping vacuuming in the hall. In the United Arab Emirates it was the Islamic call to prayer. In London it was the couple having sex next door. At Disney it was the little kids running in the hallway. You get the point. You have no idea what new sounds there will be and no way to anticipate them. Bring the ear plugs.
10. Snacks - Go get cereal bars, protein bars, nuts, or dried fruit from the store and pack some in your carryon and some in your luggage for the return flight. You never know what kind of $hit-on-a-bun the airlines will serve, if anything at all. And you probably don't want to spend $5 on a bag of chips in the terminal or $10 on the plane for something that costs $0.75. If you are traveling during the holiday, bring a bag of candy with you and give some to the airline staff when you check in. It lightens the mood and it might help you score an upgrade or a better seat. This tactic helped me score upgrades to Hong Kong from San Francisco. I still had to use my miles, but the person became willing to help instead of dismissing me and I didn't have to pay any change fees.