If you're comfortable with command-line UIs, git-annex is worth a look for creating repositories of large static files (music, photos, pdfs) you sync between several computers.

I use regular git for pretty much anything I create myself, since I get mirroring and backups from it. Though it's mostly text, not audio or video. Large files that you change a lot probably need a different backup solution. I've been trying out Obnam as an actual backup system. Also bought an account at an off-site shell provider that also provides space for backups.

Use the same naming scheme for your reference article names and the BibTeX identifiers for them, if you're writing up some academic research.

GdMap or WinDirStat are great for getting a visualization of what's taking space on a drive.

If your computer ever gets stolen, you probably want it to have had a full-disk encryption. That way it's only a financial loss, and probably not a digital security breach.

It constantly fascinates me that you can name the exact contents of a file pretty much unambiguously with something like a SHA256 hash of it, but I haven't found much actual use for this yet. I keep envisioning schemes where your last-resort backup of your media archive is just a list of file names and content hashes, and if you lose your copies you can just use a cloud service to retrieve new files with those hashes. (These of course need to be files that you can reasonably assume other people will have bit-to-bit equal copies of.) Unfortunately, there don't seem to be very robust and comprehensive hash-based search and download engines yet.