__Health__
Melatonin. There is no other way for me to go to bed and this knocks me right out (I use 0.2 - 0.4 milligrams).
Sleep mask (no more waking up because a stray light hits my eye)
I'd say sleep earplugs but I have a sound in my ear, but otherwise earplugs
Mosquito repellent scent (for sleep as well).
Silicon earplugs when going out, I never thought I'd get ear/hearing damage because I didn't go out a lot. I was wrong. They protected my ears after I noticed I got some ear damage.
A dumbbell (used at times between breaks to move a bit)
__Other__
Fuet (another HN'er once posted this as such at some thread years ago I can't remember, and I agree). It's a sausage and IMO too good as a snack.
LG 4K monitor for about $350
Moving labels. Got a bunch of moving labels for a few bucks, and slap them whenever I need to label something. Apparently, I tend to label my external HD's mostly and a few boxes that have specific items in them (e.g. only USB cables or power cables, etc.).
Not a purchase but a lifehack and since I see many responses are about cables I guess it's relevant ;-) Instead of spinning your cables in a circle, spin them in a figure 8 (two circles). Somehow it's harder for them to get weirdly tangled when you store them like that. See: https://youtu.be/buVUvnM_AzU?t=104 (I don't use the other life hacks :P)