Access your files remotely on a USB drive plugged into your AirPort Extreme or Time Capsule. Turn on Back To My Mac on in both your AirPort Utility and in your Mac’s iCloud preferences.
Now when you are outside of your network you’ll be able to see your AirPort in the sidebar of Finder as if you were still on your local network.
Note: only works on a Mac with Lion or higher. Performance or ability may depend on your router configuration. For detailed instructions see Apple’s article: http://support.apple.com/kb/HT3486