The only knife I have from either of my grandfathers: a Case CV small stockman in worn red bone that was manufactured the year my father was born! Absolutely priceless... although my first knife, a Buck 110, would be second place. And the third would be my Old Timer "Colt" orange single-blade liner-lock trapper.
After I throw all my knives away, I'll just go buy new ones again. But my memories from the three knives mentioned above just can't be bought.