How To Pack It > Checking Bags
Although carryon travel is a significant benefit of travelling with one bag, not everyone chooses to exercise this option. Further, the rules for carryon baggage vary (especially on smaller aircraft and in out-of-the-way places), and you are at the mercy of capricious transit personnel in any case. So there may be situations where you choose — or are obliged — to check your bag.
Prepare for this eventuality when packing, by ensuring that those items that you absolutely must not lose (or might be damaged in a checked bag) remain with you when your bag cannot. Your daypack will come in handy here; make sure that it is readily accessible, and contains these critical items. Of course the most critical items should be in your security pouch anyway.
If You do Check Bags... Useful Things to Know
A surprisingly high percentage of lost and stolen luggage (87% in one year) originates at curbside check-in stations; avoid them.
The most common cause of mis-routed bags is gate agent error; know the three-letter code of your destination airport (LAX, ORD, JFK, LHR, etc.), and verify it on the luggage tag before your bag vanishes down the conveyor belt.
Luggage festooned with tags & stickers announces that you're a frequent flyer; thieves target such bags, assuming wealthy travellers.
If your bag does not have some distinctive visual feature, think about adding one (this can be as simple as some coloured yarn or cloth attached to the bag handle). Doing so makes it easier to spot yours among the countless black bags that arrive at the luggage claim area, and helps thwart the thieves who would like to make off with it before you realize that it's gone.
Understand that the security of checked baggage is dubious at best. Some airlines require that such bags be left unlocked, to facilitate inspection. Others suggest the use of special "approved" locks that can be easily opened by security personnel. Nobody, however, offers any guarantees as to the honesty of security personnel; there have been numerous reports showing that the methods used to recruit and train such people leave a great deal to be desired.
The use of padlocks on luggage introduces an additional — and less obvious — problem, that of damage caused by airport baggage handling systems, in the following manner:

Finally, remember that you should be concerned not only with the issue of items being removed from your bags, but those being introduced as well. This is of particular concern to international travellers: a number of reported cases have involved the transport of contraband goods in the checked luggage of unsuspecting passengers. There are even cases where people have been imprisoned because of what is claimed to have been articles introduced into their checked bags. Such occurrences are, fortunately, pretty rare. They do happen, though, and it would be foolish not to consider the possibility of their happening to you.
"Mishandled" Baggage: What are the Chances?
The odds decline further in Europe, where the 2007 average is 1 in 60. In less developed countries, the odds get worse still. In 2007, more than 42 million pieces of luggage were "mishandled" by the world's airlines (about 80 bags/minute, 24 hours a day, every day). That's one bag for every 54 passengers, according to SITA, which tracks and reports such industry information.
When is "mishandled" baggage actually deemed lost? There are no government regulations stipulating this time interval, though the Montréal Convention says it should be 21 days after it disappeared. Further, many travellers have rather naïve ideas about the compensation due them for such mishaps; a helpful overview published by the Air Transport Users Council (the UK-based consumer watchdog for the airline industry), entitled "Mishandled Baggage", offers illuminating reading in this regard. Additionally, realize that airlines won't compensate you for any electronic items that you claim were in your bag, not to mention a host of other types of valuable belongings (usually listed in the fine print on their respective Web sites).
