Turn off All of Your Automatic Updates (Background Refresh)
Many apps will push new content and automatically sync that new information to your iPhone. It’s a convenient feature when you’re at home, but it eats deeply into your expensive data plan and battery life when traveling abroad. So head to Settings and review your apps to make sure none of them are set to send push notifications or sync data before you leave. This way, your apps will only update when you open them and ask them to, preventing any unpleasant data surprises.