I travel a lot. In the last two years I've taken easily over 100 trains (with half of those trips lasting 7hs or more), 20 overnight buses (12hs in each direction), two intercontinental flights, and I even biked to work once.
I would have to be an idiot to travel this much without learning anything. And while the jury is still out on whether I'm an idiot, I did learn some tips and tricks that I'd like to share with you.
Before you even leave your place, it is important to put yourself in the right state of mind. So close your eyes, breath deeply, and tell yourself:
"I don't know how, why, or when, but of this I am certain: someone is going to fuck it up. I have made my peace with this, and I will not let it ruin my day."
You would be surprised of how useful this mentality is. It will lower your blood pressure, make you less angry, and more importantly, will naturally lead you to "safer" choices: if you already assume your future plane will be delayed due to acts of nature, you won't book that risky 30-min airplane connection.
The secret to a good trip (or, at least, a less miserable one) is to be prepared, and your bag is where it's at. Unlike common wisdom, I'm going to suggest you get a small-ish one. How small? Enough to fit underneath the seat in front of you in a plane: boarding a plane is stressful enough without having to fight for overhead storage, and the last you want is traveling without your gear because the plane is full and your big bag was sent to cargo. And traveling light is always good.
A controversial opinion: check your allowed bag dimensions and weight, and stick to them. I know neither passengers nor airlines give a damn, but once in a blue moon an employee decides to check and it will probably happen in your trip (see previous section). I know of a bus company that makes a non-insignificant amount of extra money simply by enforcing their rules.
If you are traveling internationally and/or by plane, I recommend you also get a travel document holder like these ones. Keeping all of your documents in one place (plane tickets, ID, Passport, itinerary, emergency money, credit card, ...) will simplify your travel, and can be taken in and out of your bag in a second. I recommend one that fits A4 pages, since most tickets are printed nowadays at home.
If your have an overnight trip, then your list should start with...
- Earplugs and sleep mask: they take almost no space, are very cheap, and are ridiculously helpful for overnight trips.
- Water bottle: nothing fancy, just enough for when you wake up at night with a dry mouth thanks to the AC.
- Good travel pillow: notice that I said a good pillow. Forget about that U-shaped garbage they sell in airports - if it doesn't close at the front, you'll wake up several times either when your head falls forward or when the pillow slides away. I got one from this list, and I'm quite happy with my choice.
For long trips in general, I also like to have a good set of headphones. Over-ear (and, even better, noise canceling) are my favorites because they block outside noise by default allowing me to use a lower volume setting, a small act for which my hearing will be thankful 20 years from now. They can be bulky, however, so I encourage you to shop around for the right model for you.
First-timers will always take the window seat. This is a perfectly reasonable choice: they want to enjoy the view. Veterans, on the other hand, know that the hallway seats are where it's at: windows lose their charm after about an hour, but standing up and walking whenever you want never gets old. And unless your plane/bus/train is full, other passangers would rather try other rows than voluntarily sitting between the wall and someone they don't know.
You should also seriously consider taking your shoes off. You can find some light slippers to bring along, but at this point a warning is mandatory: you must ensure (and I shouldn't even have to say it) that you are wearing clean socks and that your feet don't stink. Don't be that guy!
Finally, boredom is your enemy. Forget that difficult novel, your work notebook, and that expense report you've swearing you'll start once you have free time. Bring a book you like, that series you've been meaning to watch, or pretty much anything you already know you'll enjoy.