Splinter of the Mind's Eye
In retrospect, it's hard to believe that the original Star Wars film, A New Hope, would be anything but a roaring success—it's got adventure, laser swords, robots, spaceships, mysticism, and Carrie Fisher, after all. And yet when it was first released, sci-fi movies were in a bit of a slump, and neither 20th Century Fox nor George Lucas were sure how A New Hope would play to audiences. Lucas always wanted to do a sequel (at the very least), and so he had a contingency plan: if Star Wars was successful, he had a script for The Empire Strikes Back ready to go—as vast and epic as the first Star Wars. If it flopped or was a more modest success, however, Lucas had Splinter of the Mind's Eye at the ready.
A far less grand story, the plot finds Luke and Leia wandering around a swamp planet, trying to find a talisman that makes the Force more effective. At the end, Darth Vader shows up for a lightsaber battle; Han Solo doesn't show up at all. A screen adaptation of the story would be so low-budget, Lucas figured, that the studio would probably let him make it, even if Star Wars was a bomb. Bonus: If Star Wars worked and Empire got made, then Splinter of the Mind's Eye could easily be turned into a Star Wars novel—he'd even gotten Star Wars novelization author Alan Dean Foster to write it. And that's exactly what happened.