Travel! Travel! Travel!
Extended travel is one of the most beneficial things you can do. On top of seeing a lot of cool places and meeting awesome people, when you spend a few weeks, months, years in a new place you learn about yourself. You are forced to leave your comfort zone as never before as you figure out how to live your life in a new place. Having to meet new people, learn a new language, navigate new streets, or even just figure out a grocery store so you can buy what you need are just a few of the challenges you will have to face in order to be successful. I've spent extended periods of time in different places in the US, Germany, and Peru and can say from experience that living abroad teaches you to be adaptable, think on your feet, and to cope with situations in which you may feel extremely uncomfortable. It will help immensely with your personal development and make you a more interesting and valuable human being. So get out there and see the world!