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.
A Packing List
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 "Day Travel Bags" section.
Women who take the time to investigate can find small cosmetics bags that do excellent double duty as clutch purses.
lightweight duffel/laundry bag
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. My own solution (pictured at right), Easy Going's "Last-Minute Bag" — 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) — is no longer marketed. But Sea to Summit's Ultra-Sil Duffle Bag provides a capacious 40 litres (10.5 gallons) of storage in an even lighter (80g / 2.8 oz.) package.
The true minimalist will consider combining this functionality with a light, roomy daypack.
luggage lock(s) (cable?)
In all situations when your separation from your bag is more than brief, it's important to appreciate that luggage is inherently insecure, thus not a safe repository for valuable items. Nonetheless, there are certainly precautions you can (and should) take to discourage casual pilferage.
Theft from bags stored in overhead aircraft lockers — especially on overnight flights — 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). And it's not a bad idea to store luggage in the overhead compartment across from you, rather than above you, in order to keep a closer watch on it.
Luggage locks are easily compromised, so don't expect much of them. Keyed locks are fussy to deal with and prone to key loss, 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 possibilities 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 split key rings (such as shown at left), nylon cable ties (available from electronic supply stores), or even a sturdily-knotted length of dental floss, but proper padlocks are more convenient. That said, it's wise not to use (dangling) padlocks on checked bags, else an airport conveyor belt may remove them 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 many require the use of specially approved locks that can easily be opened by security personnel (and anyone else with a simple tool). Go figure.
Should you wish to take a short nap, or be briefly apart from your bag, augment your lock with a simple security cable, which lets you secure it to a large or immovable object (or even to other bags, which is better than nothing). 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 right) is more practical than a fancy one with an integrated lock, as a separate padlock can easily be replaced/upgraded/re-used as desired.
A less secure, but still useful alternative to the cable — if you're not planning to leave your bag unattended for long — is the use of a mountaineering carabiner (which has multiple uses, always a plus).