Gmail has introduced a new feature in Gmail Labs which will allow you to send attachments when you are in offline mode. Offline mode allows users to download emails and read them in Offline mode in a web browser, the emails are stored locally by Google Gears.
Earlier, Gmail only allowed users to compose email while they were in offline mode, and sent it whenever they were connected to the internet. However, they have now also enabled uploading attachments while in offline mode.
What this means is that, you can now quickly download all the photos you took on your trip and attach it while you are on the plane. The email and attachments will be instantly sent out when you have access to an internet connection, saving you both time and efforts and giving you something interesting to do on the plane.
To make use of this feature go to Gmail -> Settings, and enable Offline Gmail.