Maggie's Farm

This happened to T.E. Lawrence, too. He lost the first draft (and only copy) of Seven Pillars of Wisdom on a train.

From Wikipedia:
"Lawrence kept extensive notes throughout the course of his involvement in the Revolt. He began work on a clean narrative in the first half of 1919 while in Paris for the peace conference and, later that summer, while back in Egypt. By December 1919 he had a fair draft of most of the ten books that make up the Seven Pillars of Wisdom but, in an act of monumental absent-mindedness and misfortune, lost it (except for the introduction and final two books) when he misplaced his briefcase while changing trains at Reading railway station."

Lawrence had made extensive notes during the campaign, which he had destroyed after writing the draft. He therefore had to reconstruct the book from memory.