Flying on an airline is probably more stressful now than it's ever been. Most people are still a little worried about terrorist attacks. And if they're not worried about that, then they're worried about getting beaten senseless by the airline employees.

So how do you combat stress on a plane? By packing one simple item into your carry-on bag...a tennis ball.

According to a writer at the magazine Travel & Leisure, a tennis ball is the perfect item to give yourself a back massage. Just put it behind your back, lean on it, and roll it back and forth. Even if you don't have a bad back, it help increase blood flow, and helps fight off jet lag. You can also use it on your shoulders, arms, legs, and feet.

They also recommend getting up, stretching, and walking if you're on a long flight.