A little silver bracelet my father gave me when I was born.
I'm a hopeless sentimental, so beyond that, I have stuff from the precious to the ridiculous.
My childhood bible, teddy, gloves, and other mementos going all the way up to high school love letters, hotel keys, favorite college shoes, and a lock from my son's first hair cut.
Not to mention loved ones old mementos - and books!. I just can't bring myself to throw away anything that evokes a sweet memory.