One of the most important things the military teaches new recruits during basic training is the importance of drinking water. At all times soldiers have to carry water -- either in canteens or in jugs in the vehicle -- to stay hydrated. But of course, you don't have to be a soldier to get dehydrated.
When traveling across time zones, dehydration can sneak up on you if you aren't careful. The quickest way a vacation or business trip can take a turn for the worse is if you need to spend a night in the hospital taking in intravenous fluids. Keep yourself hydrated throughout the entire travel process.
Drink lots of water. Stay away from the energy drinks and sodas while traveling -- especially the energy drinks. They may seem tempting, but energy drinks don't provide significant help in replenishing your body's fluids. Stick to water before you fly and during your flight, too. And drink plenty of H2O leading up to the flight. Not only will you stave off dehydration, it's free once you're on the plane.