Currently, there isn't an easy way to back up your Hubs in its entirety. There are essentially three things you can do that will provide essentially easy back up's if for some reason Hubpages shuts down or your account is terminated.
1. Save all the text in word/notepads in a folder with all the images used (assists) as if this was your own webpage.
2. In firefox and other browsers you can right click and "Save Page As..." which will make a folder+an icon that will launch the page in your browser even if your not online. (local files)
3. Save the page as a PDF using the Print function. Using Adobe Acrobat Pro you might be able to convert the text into editable text to copy/paste.
These are the only three options you have that you might be able to simply copy+paste the text copy. If you wish to just have it you can print the page out but if Hubpages went down or your account is terminated you will have to retype the text copy and re-find the photos used.
Hope this helps you and everyone else out!