Something that maybe got lost in a house move, left behind when you left home, broken, or that you didn't realise how much you loved until years later. Something that when you think about it now fills you with nostalgia.
Mine is the sun/moon face watch (day/night as opposed to a classic moonphase) that my mum bought me for my 16th birthday in 1988. They were such a thing then and I loved them so much. She got it from the catalogue and was still paying for it by my next birthday bless her. DD bought me a version of it for Christmas and I absolutely love it, but I wish I had the original too.
Also my original Magic Faraway Tree books from the 70s.
What's yours?