In sheer monetary terms, my car.
In terms of possessions... I like all my stuff too much to throw it out. It all means something to me. By that definition all and none of it is precious.
My camera, when I do my "pretending to be a reasonable photographer" thing, makes me more confident, more likely to go places I wouldn't have before just to get a good picture. I might speak to people I wouldn't otherwise speak to.
My computer keeps me in touch with almost everyone I know. Far more so than my phone. If it weren't for my computer I'd either feel far lonelier, or I'd be out there having a life. Maybe I should try it some day.
I don't really own many special things. You would have to fight me to the death to get me to part with my books. Stacks and stacks of books.