Oh...this is easy.
My album collection...
Not that it was so large (maybe 150-200 max), but I was an apartment dweller back then so I moved around a lot, and I was tired of lugging them from place to place. Went I got my 1st real hifi system, I was all in on CDs...when I was ready to leave FL for NYC, my ex-roommate ask if I was taking my albums and I said no, how much will you give for all of them...iirc it was about $100.
Now, vinyl is back and I've moved on...part of me regrets that.