Anything no matter how big or small. Personally wireless headsets/phones have been a huge quality of life improvement for me

I would say noise canceling headphones particularly wireless.  My wife and I enjoy listening to music throughout the day, but sometimes different genres.  Headphones solved the problem.

I have two that I can think of:  The Ryzen 9 5950X and my EVGA RTX 2080 TI XC Black. 

 
Moved to Hardware.

Evga GTX 1080ti has served me dang well never an issue unless
it was mine, still working but I never bothered oc it. And always
gave it plenty of air.

I don't know if this qualifies as a "tech purchase" but it's a fundamental part of my gaming setup: A damn good chair.
 
I picked up a Steelcase Leap v2 (~1000$ MSRP) from a local furniture liquidator for about 350 $USD after a ton of research and a thorough inspection.  It's got a ton of adjustments that I have set once or twice, and never touched again. It doesn't blow your mind when your ass first touches the seat, but my god, it has transformed my outlook on working and gaming at my computer. Good ergonomics are worth more than their weight in gold. I used to have a $250 "ergonomic" office chair that I thought was pretty good. I would have back, shoulder, and neck pains after long gaming sessions. What I was saving in cash on each chair I would pay for in physical discomfort. On top of that, the chair would wear out and I would need to replace it every few years. I don't really care if Steelcase won't honor their 12-year warranty because I'm a secondhand owner. I'll just get another "gently used" one from a reseller. 
 
I'm in a better mood and more relaxed when I'm gaming because I'm physically comfortable the entire time. I can work longer, play longer, enjoy it more, and step away from my computer without feeling exhausted. I don't need to budget energy into my gaming sessions anymore. I can still play if I am tired, and I will feel physically OK afterward. It feels good to invest in my physical health.
 
If you can afford it, please get a GOOD chair that you can sit in for an entire day without ever feeling a single ache or pain. Then pledge not to because you're supposed to take breaks, and break that pledge by sitting in it for hours at a time anyway, because who are we fooling here? We're gamers. There are very few brands worth looking at with the a solid service and reliability record. Steelcase and Herman Miller lead the pack. Everything else is a cheap imitation or not designed for use at a desk (I'm looking at you, racing chairs).
 
**** the hype. If you're gonna sit at your computer, buy the stuff that companies provide their engineers to sit in. These are the chairs companies use to protect themselves from RSI injury lawsuits. They're damned good.

I got a used 1080 on ebay for under 400 when the price of crypto took a short dive. Prices are back up to around 500-600 for the same card now.

LeChuck81

Chabbert
a little 3.5" display that runs goverlay

Please, tell me more.
[insert Willy Wonka's meme here]
 
No, seriously, I'm genuinely interested in this, was looking for a mini hdmi display to put into the dual 5,25" front slots as a case mod inspired by this JayzTwoCents video
 

Here I use this on an old tablet works great takes a bit to figure it out tho might not fit where you want it.
The tablet sits under my monitor. giving them a couple bucks donation is oh so worth it
 
https://www.youtube.com/watch?v=Um6B4XX6-qI

Just built my first PC this past weekend.  Hard to say which elements is the BEST.  I'll go with the 5900x, but the Lian Li O11D Mini is a close 2nd.