One foundational precept of programming is to separate code, content and layout. Thus CSS was developed, allowing one to set the parameters of web page elements separately from the content of the web page, which allows one to even change the look of the page without changing the contents of the page, on the fly.
The same can be applied to computers. Separate your personal files from your OS files. Your internal drive needn't be huge, it only contains your OS. Small and fast would be better than huge and slow.
Your personal files would reside on an external drive, so if something were to happen where you had to flee suddenly (wildfire, flood, tornado, riot, stampeding rabbit horde, etc.), you just grab the hard drive(s) containing your personal files and go.
Thus, you can wipe the internal drive and reinstall the OS without losing your personal files. Of course, it would be a good idea to save your personal files on a file system that multiple OS's can access... so FAT32 or NTFS.
Or, barring that, have your personal file storage set up as a NAS box... grab it and go in an emergency, then plug it into any network and your files are accessible (no matter what file system the NAS box uses); and with proper security, you can access your personal files remotely from the internet.