Having an up to date backup can save you from many troubles. Using Magento I would suggest you to backup the entire site. You can use your hosting panel and create a compressed .zip of all your public folders.
Perhaps this option will force you to download a couple of GB’s of files and folders. The Media folder Surf your site using a FTP client and go to /media/catalog Backup that folder wich contains all the product images. Database Backup You can use the build-in feature to create a database backup from the Magento admin panel.
Go to System -> Tools -> Backups Now you have to Create a Backup and then download it.