Assuming it's a common 1TB, and assuming I have peripherals like keyboard, mice, headphones, etc.
-small, simple, and stable OS with up to date packages and software to run whatever I'm storing
-vidya, probably from older generations like gameboy and NES because the files sizes are so tiny you could have tens of thousands in a few gigs
-couple hundred thousand books (mostly in plain text format except for documents that need pictures), everything from science to novels to instruction manuals and survival guides
-infographs about ammo size or first aid or whatever I might need
-music, probably enough to take up 100GB or so at moderate bitrate that will give enough variation for all kinds of moods I'd be in
-depending on how much space I have like ~10gb of porn in pictures
-leave like ~50 gigs freespace for documentation: journal, pictures, video diary, etc.
If the HDD is smaller like 500gigs or less I'd probably most free space and keep a pure text journal, omit some music and porn