Kemco Music Recorder MP3 - very weird  MP3 player / audio recorder with line-in(!) / kareoke overdubber cartridge for GB Advance:
https://www.ebay.co.uk/itm/123774520359

2 x Mega Memory Pak ( I bought these with the idea of shooting 100s of full Gameboy Camera rolls for animation purposes but never used them, could be used to back up and copy chiptune savs I believe but don't use LSDJ so can't promise)
https://www.ebay.co.uk/itm/123774482468
https://www.ebay.co.uk/itm/123774492442

Game Downloader serial flash cart / copier thing, never had the time to figure out how to even use this but it comes with enough free gameboy to serial to serial to USB cables to choke a horse so I'm sure one of you can figure it out
https://www.ebay.co.uk/itm/123774435289

NES Game Genie. Had fun making Super Mario produce free jazz back in the day but no longer have and NES
https://www.ebay.co.uk/itm/123774541970

I set these as UK postage only on ebay due to too many weird delivery mishaps and fake buyers internationally, but I trust you peoples so message me if you realllly want any of this outside UK and I'll see what we can do.

Probably listening more gameboy / circuitbending/ game stuff soon too: https://www.ebay.co.uk/sch/timdrage/m.html