Glaring at the mother of the squalling baby in the airplane seat next to you may feel good for a moment, but it doesn't help the situation. Smiling and offering to help does your soul a world of good -- and helps your stressed-out seatmate to boot. Take that attitude of kindness and compassion with you throughout your journey. It's the most useful kind of carry-on luggage to have. Not only that, but it might bring you a surprising contact who can lead you to a sight you never would have known about if you hadn't been so actively big-hearted.