TLDR: Keep multiple copies across multiple mediums.
But what does this actually mean?
This means creating copies of your files and saving them in different places. For example, you can save a file to your computer then send it to yourself and keep it on your phone. This means that if one device fails (e.g. you spill water over your laptop) you still have a second copy of the file.
A better solution would be using an cloud service. These are free (e.g. Google Drive, OneDrive, Dropbox) and come with enough storage to upload any files or evidence you may have. You probably have access to one of these services already if you have an existing Google or Microsoft account.
Keeping your files on the cloud means that you can use it on your phone and laptop, you also don’t have to worry about keeping versions updated.
If you do use a cloud service, make sure to still make regular copies of your work and keep them on your phone/computer. Consider copying and backing up your files to another cloud service provider too.
For example, you have a Microsoft Word (docx) file. You keep this on OneDrive so that you can use it on your phone and laptop. It would be good practice to regularly create a copy of this document and keep it on your laptop and upload a copy to another service like Google Drive.
This means you have copies of your files across both a physical device (phone or laptop) and across multiple cloud providers (Google or OneDrive). This will help protect your data from accidents or natural disasters.
If you want to learn more about back ups, check out the NCSC’s page.