You've made all your travel arrangements, your neighbor's all set with a key to get in and water your plants. All that remains is to pack your bags and show up at the airport. Before 2001, this meant just stuffing your bag the night before and getting yourself to the gate. Now, all carriers with a departure or landing point in the U.S. randomly select a percentage of each flight's passengers for vigorous security screenings. Casual and careless packing won't do.