Man, alone of all the creatures of the world, carries baggage. Animals often carry food and building materials to their "nests". And they sometimes migrate to distant points, but they carry no baggage with them. People, on the other hand, are apparently never so primitive that they do not carry something in the way of baggage. This and speaking a language are their most exclusively human traits.
Packing List
Luggage
travel pack or shoulder bag (& luggage cart?)
This topic is discussed at some length in the various "What To Pack It In" sections.
daypack (fanny pack? purse?)
Daypacks are covered in the "Leisure Travel Bags" section, although many business travellers (myself included) find them every bit as useful.
A (light, strong) nylon bag will isolate your dirty laundry until the next washing. More importantly, it can be used as a second bag if necessary to bring extra stuff on your final flight home: simply check your principal bag, and use the duffel to carry your more fragile/valuable items aboard the aircraft. An excellent (albeit no longer available) example is Easy Going's "Last-Minute Bag" (pictured at right), which weighs about 3.5 ounces (100g) and folds into its own side pocket, measuring about 6 × 8 × 0.6 inches (15 × 20 × 1.5cm).
The true minimalist will consider combining this functionality with a light, roomy daypack.
luggage lock(s) (cable?)
Your bag should have zippers designed to be locked with a small padlock. Which you should use accordingly, to keep the contents from the prying fingers of airport hangers-on and street thieves, not to mention the curious eyes of your B&B host's children. And theft from bags stored in overhead lockers on aircraft is a lot more prevalent than you might think, so take precautions there as well (if a bag entry point is not secured, turn it to the rear of the storage compartment). Make sure to lock all entry points to your bag, especially in poorer countries.
Keyed locks are fussy to deal with, more easily compromised, and prone to loss of the keys, so use the combination variety; for checked baggage in particular, select a lock with at least four combination wheels (it takes a surprisingly short time to cycle through the limited possibilites of a three-wheeled lock). Letter-based locks make combinations more easily remembered for some. Casual pilferage can often be avoided by securing bag openings with nylon cable ties (available from electronic supply stores), or even dental floss, but proper locks are more convenient.
Should you be forced to check a bag, it's wise to remove (dangling) padlocks, else an airport conveyor belt may do it for you!
It's worth noting that some carriers will not accept bags as checked luggage unless all external openings are locked. Some will not accept bags if they are locked. And some require the use of specially approved locks that can by opened by security personnel (and anyone else with the correct tool). Go figure.
A locking cable lets you secure your bag to an immovable object (or even to other bags, which is better than nothing), in case you need to be apart from it briefly, or take a short nap. This can save you from "snatch and grab" thefts, and is sometimes a useful technique on trains and other public conveyances. A simple cable (as pictured at left) is more practical than a fancy one with an integrated lock, as a separate padlock can easily be replaced and re-used as desired.
In all situations when your separation from your bag is more than brief, however, remember that luggage is inherently insecure.
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A one-page checklist version is available here.