If you never manually imported an account key into your wallet, you can alternatively backup your accounts and their funds by exporting the brainkey, a string of words from which your keys are derived deterministically.
To create it, you should do the following:
1. Go to settings
2. Choose "backup"
3. Choose "create brainkey backup"
4. Enter your password. Press "show brainkey"
5. Save your wallet brainkey.