In my early twenties, I was very good about keeping a copy of my passport in a separate bag from my actual passport. Then I got lazy. Recently, a friend of mine lost her passport at the airport. She was told that if she had brought a copy of it and extra passport photos they would have let her travel. Since she didn’t, she was forced to forfeit a $2,000 flight and a week in Europe. I now carry a copy with me.