You want a menu? Edit the menu file.
You want a toolbar adjustment. Edit the toolbar config file.
You want a unity style launcher, edit the slit and get dockapps... oh and don't forget to load your own icons!
However once you have done all that, you ship our system (i.e. your homefolder) to a backup drive or dropbox and
you are set for as long as they keep supporting fluxbox.
Oh and did I mention it was lightning fast?