Travel. Extensively. You will never regret it, you will always remember it, and you will always have a story or 10 to tell people when socializing. Parts of the developing world (India, Thailand, parts of South and Central America) are still cheap enough, and interesting enough, that you can get by on $1,000 or so a month while still living relatively well. I spent several months traveling >4 years ago while transitioning between both job and countries, and still talk and think about it often.