Although James Bond's black attaché case came equipped with knives and tear gas, the more ordinary version is still a spectacularly useful thing for the avid traveller to carry.
It is small, relatively compact, very light when empty, and not hugely heavy even when full. You can also be sure that if a large person sits on your attaché case, the contents are unlikely to be crushed into a pulp.
You can fit a surprising amount of belongings into one: clothes (a whole suit if you're lucky), shoes, pens and pencils, books, travel guides and train timetables, writing pads, wash bags, towels, emergency food supplies, eating utensils, laptop computers, GameBoys, and boxes of tissues - although not necessarily all at the same time.
An attaché case can also be used for defending oneself from attack. It can deflect projectiles and falling masonry, and makes a handy step if escaping from a high window.
It can also be used as a weapon. A briefcase can be thrown short-to-medium distances (its sharp corners are very useful in this respect), can be used to make rudimentary swipe and thrust attacks, and you can also bash somebody over the head when they're not looking.
An attaché case can also be a lifesaver when one is called on to wait for a long period of time and no seats are available, allowing one to sit on it and rest one's weary feet. Finally, if push comes to shove, wrap an attaché case in your towel to make a comfortable pillow to bring about restful sleep.