I love how you are building up the AskSteemit group. It's one of my favourite parts of Reddit. As for an answer to your question:
An album of memories shared between my girlfriend and I. There are drawings, photos, tickets and other irreplaceable items.
My harmonica. My house just burnt down. I'm gonna need to make some money somehow.
Honestly, my folder of documents. This includes my degree, birth certificate, passport, and multiple keys/passwords for cryptocurrency wallets.