Harry Harrison & Robert Sheckley 
Bill, the Galactic Hero on The Planet of Bottled Brains [EPUB ebook] 

He’s the perfect starship trooper: big, strong, and not too bright. He’s the perfect hero: willing to do almost anything to save his neck (it’s one of the body parts that’s still his own.)Tsuris, the Mystery Plane, has a mysterious secret weapon, and Bill must get it. But Bill has something the Tsurisians want. They have a lot of brains, but not enough bodies. They’ll take any body that comes along – and put one of their brains in it!Can Bill escape with his own brain? Can he find the secret weapon? Can he get a drink?