Jumping down a steep evacuation slide from a burning airplane with people all around panicking isn't easy, and you need your arms and hands to help. Yet time after time, passengers evacuate toting suitcases, laptop computers and other valuables they apparently can't leave behind.

Images from the crash landing of Asiana Airlines Flight 214 in San Francisco showed some dazed passengers fleeing the Boeing 777 wreckage with carry-on bags and iPads. One even had two boxes of duty-free alcohol. Some ran in shoes with heels—another...