Go into Account Settings and under Personal enter an e-mail address, and then an Alias,
Then below Personal is General, click on that and mark the checkbox for Automatic Email Backups.
You'll get an email with an encrypted backup of your blockchain.info/wallet. It will be sent each time it adds a new address so you may get these frequently if you use Custom send and specify that change goes to a New Address each time. The backup file is an attachment to the message, called wallet.aes.json
You might also want to set a second password if you haven't. That's under the Passwords link on the left menu panel. This second password will be asked each time you want to spend from your wallet.