I agree with Jmax, you can delete alot of your stuff , which I am pretty sure you will never need.
But if you really need all the data or feeling lazy there is a very fine tool at your rescue.
Go to Savemyinbox and install the tool on your machine , give it credentials to your dropbox account (create one if you dont have one ) and your gmail account.
It will backup all your mails to dropbox which you can then access from anywhere.