In Unity 4.x and earlier, I was able to open the editor.log file after a build, find “Player size statistics”, and determine what is contributing to bloated file size (if anything). In Unity 5, this information is no longer part of the Editor log… where did it go?
My mistake. I was building for the webplayer, but my webplayer build had errors, so it never got to the point where it would spit out the webplayer size. Oops.