Simply install Google Chrome on your Mac or Windows machine and download the Offline App from the Chrome store for free.
Then, while on a plane without Internet access or even before turning on a battery draining WiFi card in a laptop or mobile tablet, prepare emails in Google Offline and access your calendar and documents (documents have not been made editable offline, but they are working on this to get make it available ASAP).
When completed with your emails, reattach to an Internet WiFi hotspot (that is WPA/WPA2 protected!!) and send your emails.
According to the GMail team's recent announcement:
Google Calendar and Google Docs let you seamlessly transition between on- and offline modes. When you’re offline in Google Calendar, you can view events from your calendars and RSVP to appointments. With Google Docs you can view documents and spreadsheets when you don’t have a connection. Offline editing isn’t ready yet, but we know it’s important to many of you, and we’re working hard to make it a reality. To get started using Google Calendar or Google Docs offline, just click the gear icon at the top right corner of the web app and select the option for offline access.
This again shows how forward thinking Google is with their cloud technologies. For those mobile professionals looking for this technology built into their mobile devices, consider the laptop replacement called the chromebook. It comes in both wi-fi and 3G releases.
