Bring a book, music or a movie to distract you while you are traveling. It takes you out of the present moment and all the stress that goes with it. It's me time at 30,000 feet surrounded by strangers. It really is.
Avoid red-eye flights when possible. Those overnight flights seem like a great idea, board your flight, go to sleep and wake up where you're going. Unless you can sleep anywhere, anytime, in any position you need to rethink that. It may be unavoidable on an international flight and there are ways to minimize the discomfort but there's no substitute for a bed. It's hard to arrive refreshed and ready to start your day when you've just crossed 3 or more time zones with 2 hours of REM sleep.
If your travel involves a schedule you're not used to, acclimate yourself before you go. If you're going to be walking a lot, then start walking more about a month in advance of the trip. Eat a good healthy diet before you go to build up your resistance to colds and to boost your energy level. You can't always control your diet while you're traveling, but you can before you go.
Forget the idea of losing 20 pounds before you go, or buying clothes for a body you don't have. Do what you can to feel as comfortable as you can on this trip so you can enjoy every minute of it. But don't set unrealistic goals.