Upvote:3
One way might be to carry a PLB (Personal Locator Beacon) which is essentially a GPS receiver with an emergency radio transmitter, that can be activated manually or (on some models) automatically by immersion in water. These are monitored using a global satellite network and so in theory will work anywhere in the world. Certainly in Australia and the USA the search and rescue organisations understand PLBs.
Such a device is unlikely to help much in case of an emergency aboard a commercial flight, because (a) the aircraft probably has better emergency location systems anyway, and (b) you probably won't be permitted to turn on the device during flight because it has a radio transmission function.
Under non-emergency circumstances, a pretty good method is to use a smartphone with an app like Apple's "Find My Friends" or Google Latitude to keep in touch with family and friends at home. Particularly if you have cellular data service (and enough cell phone battery), this will allow people to find your location (at least, the location of your phone) quickly.
Finally, having a phone with maps helps you to avoid getting lost.