While you are researching and writing your thesis or other projects, you should actively maintain backups both your own writing and any research materials that you are working with, such as PDFs, video clips, and data sets. Here are a couple of resources that you might find useful:
Any backup plan you design for yourself should have these features at minimum:
Multiple copies of your files. For example, maintain copies of the same files on your laptop and online in a cloud service. If you have only one copy of a file, it is not backed up.
Geographical separation. Backups should be in a different place from your original files. Don't leave a backup external hard drive next to your computer, in case they both get stolen or your apartment floods. Online backups in a cloud service are one solution to this, though you should still maintain at least one non-online backup.
Reversability of changes. For your own writing, you will want to save older versions of files that you are working on, in case you need to restore something that you deleted in the revision process or in case you accidently mess up the file. Periodically save new copies of the files so that you can access the older versions. Back up these older versions as well. For example:
Cloud storage services may enable you to revert to older versions, but you should verify that capability with whatever service you end up using.