A spokeshave, Stew-Mac Dragon rasps, and sandpaper.
I like to cut a belt from my belt sander in two or three pieces, put a little duct tape on each end for a "handle" and use it to to smooth the neck after some work with the rasps and spokeshave. Belt sander belts have a much thicker substrate than sheets of sandpaper, and last a lot longer when you use them like this.