Speaking on my wife's behalf, an epipen. We're both content with not having needed to use it.

Probably 500+ bottles of expensive wine, more possibly even. Some of it was free, but most not, and it's all crammed into a 2 bedroom apartment turning to vinegar because it's improperly stored. Sometimes life circumstances mean you can't drink much anymore. So it's pretty much a waste and hugely embarrassing.

Never tie your finances to that of a crazy liar.

I got a pretty nice Yamaha bluray player that was an appropriate match to my home theatre amp.

Put a bluray in it, got a piracy warning, a few unskippable ads for other movies, an obnoxious excessively drawn out animated menu screen that stuttered like hell and was laggy to use.

Pulled the bluray back out of it, stuck it back in the DVD drawer and proceeded to download a copy of the movie to watch. Been doing that ever since.

First edition, first run of the three Lord of the Rings books.

I can’t bring myself to open them up and mess with the pages.

A pool. It came with the house, but damn is it expensive to maintain. I say I've never gotten full use out of it because I spend way more time and energy maintaining it, than I do using it.

A pair of traditional leather boots that were stiff and sturdy enough to support me through anything and last long enough to be buy it for life. The pair weighed over 5 pounds. After 6 months they still hurt after a hike and I gave up breaking them in. Cost me over 300€, and I replaced them with a pair of 80€ trail running shoes which were better in every way for my use case and also lasted 12 years.

I have a college degree I have never used. It wasn't cheap even tho much of it was paid with grants.

My 6-foot-tall telescope. I should really pull it out more, I just get so busy.

My house. There has never been a point in time where there was not at least one room unusable due to ongoing renovation.

3d printer

I bought some kit for running TTRPGs just before COVID hit: wet erase markers, Chessex mat, extra dice bags, DM screen, and some cheap minis. Then when COVID hit I adopted a Virtual tabletop (Foundry). Over the course of the pandemic, my gaming group evolved to include people from all over the province, and so now there's not really any hope of playing an in-person session. Not to mention I switched to playing PF2E, which is really hard to run in-person because of how much crunchier it is. So now I have this stuff and don't really know when I will get to use it.

I've just built a $1200 PC and I'm pretty sure I don't really use the fraction of its power.

An ecoflow battery generator. Granted, it's a small-ish one but I got this itch to purchase one after seeing one in action while car camping ("I can use my hot water kettle while camping, how cool!") and when our city was warning us about widespread power outages from an upcoming winter storm ("to keep our devices powered up").

I bought an $800 half stack guitar amplifier in 2009 and rarely play with the volume above 1, let alone play shows with it. But it looks neat.