On the one hand, there is my data, which I back up onto a portable hard disk on a regular basis (and burn to DVD often as well). In my nightmares, the fire alarm goes off and I grab that little bundle of information at the same time I am tying my shoes. If I have to jump, it's still going with me. In that little box are the pictures I've painted, the words I've written, and the rest of the echoes of who I am.
On the other hand, it's the shoe-box I keep on the top shelf of my bedroom closet. Within that little box are a scant handful of items that include a pebble from the top of a mountain I once sat upon, a small piece of a Redwood tree (purchased from the environmentally friendly park shop, not scavenged), a nut (as in nut and bolt) surreptitiously removed from an unobtrusive spot on a wall in the sound stage where Fritz Lang shot "Metropolis" in 1927, and the small collection of cards and gift tags from presents I received when I was younger, amongst other things.
Everything else is just "stuff" and I wouldn't miss it, but loosing either of the above would be devastating.
Nick