I use the note-taking app Evernote to save notes about practically everything, and that includes my travel itineraries. Evernote can keep a copy of important travel information offline. Let's say you show up at your destination and can't get any data on your phone to, say, pull up a confirmation email for your rental car or find the address of your hotel. If you've backed up a copy of the important details to Evernote--which you can do by simply forwarding emails--you'll have everything you need regardless of cell signal strength.