A preteen boy develops leukemia before medicine can help him. He leaves all of his treasures (stamp collection, etc) and a note in a time capsule for the future. It works, and someone from the future arrives to save him.
Dave Hook

Variants

(1)
  1. “The Will” by Walter M. Miller, Jr., Fantastic, January/February 1954.
  2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . written by [Error: Missing ']]' tag for wikilink]