Travel is delightfully (and frustratingly) unpredictable. If you usually bring a flashlight and some Imodium, then you already know that things can go wrong. When they go seriously wrong, how your react can determine your life span. Foreign correspondents and international aid workers often get special training. The next best thing is a back-pocket travel survival instruction manual.
I wrote such a manual for Rough Guides a few years ago. It was originally supposed to be passport sized, but at the last minute the publisher's sales reps thought it had to be thicker and bigger so it wouldn't get lost on bookstore shelves. Only problem is that made it too heavy and thick to easily toss in a backpack, which largely defeated the point of this pack-along book. I tried to protest, but lost.
Rough Guides has now wisely turned it into an app. It's got all the nuts and bolts and diagrams of the book, plus a great feature that lets you dial the local embassy or emergency services in any country with a quick tap, and it takes up no space it at all!
It just arrived at the app store and here's the link. It's six times cheaper than the SAS survival manual app, doesn't try to teach you how to tie a dozen fancy knots and covers the most important stuff you need to know for traveling off the beaten path.