Remember to bring your phone charger with you when you travel. If you are outside the US, check to see what type of plug and voltage are used in your destination. If you pack the right converters, you can charge your phone just like you do anywhere.
If you have a phone with data roaming features, you may want to turn that off before your flight. This will tell your phone not to connects to data networks outside of your home network. This also helps in keeping the data roaming charges less.
Same with automatic emails. You could be using data without knowing it. If you turn off the auto features, your charges should be less.