Gaming consoles and all of the parts for fixing and modding them. Got an OG Xbox that crashed, so I bought new caps, then I needed a soldering iron, then I got an Xbox 360 so I needed a modchip and a flasher as well as a 4TB harddrive and then I got a FAT PS3 with broken SMD caps so I needed a preheater and a hot air station and then I needed to get all of these controllers which are worn out so I needed potentiometers, thumbsticks...
I do play my PS2, PS3, Xbox, 360, One etc. all the time (they don't just sit in my room to look pretty) but yeah, I 've probably sunk thousands of euros into maintaining them. ๐
I use the equipment to repair other things I get for free or very cheap, so it's not just a money sink...or at least that's how I rationalize my hobby. Repaired a Nikon camera with it...then I bought lenses...just another rabbithole!