GOOGLE TRANSLATE
Google Translate is so smart that you can take pictures of words in foreign languages and it will translate it for you (works for Chinese and Korean as well!)
GOOGLE MAPS
Helpful in figuring out how to get somewhere even without data. You can download offline maps for later use in Google Maps.
FLASHLIGHT
Having a flashlight app is useful when you have to wake up at 5 a.m. in a 6-person dorm room for your flight and wish to escape the wrath of five angry travelers.
JETLAG ROOSTER
There are many of these calculators on the market and they’re pretty helpful in dealing with jetlag. Just input your trip information and it should work out a sleeping schedule for you to minimize jetlag.