All default Xfce menu categories are configured in /etc/xdg/menus/applications-merged/kali-applications.menu to be moved under the 'Usual applications' category. This does not happen in Xfce however.

The way to fix this is to change the following in /etc/xdg/menus/xfce-applications.menu:

1. Add an entry for the 'Usual Applications' menu ('<Menuname>Usual Applications</Menuname>')

   <Layout>
   <Filename>xfce4-run.desktop</Filename>
   <Separator/>
   <Filename>exo-terminal-emulator.desktop</Filename>
   <Filename>exo-file-manager.desktop</Filename>
   <Filename>exo-mail-reader.desktop</Filename>
   <Filename>exo-web-browser.desktop</Filename>
   <Separator/>
   <Menuname>Settings</Menuname>
   <Separator/>
   <Menuname>Usual Applications</Menuname>
   <Separator/>
   <Merge type="all"/>
   <Separator/>
   <Filename>xfce4-about.desktop</Filename>
   <Filename>xfce4-session-logout.desktop</Filename>
   </Layout>

2. At the end of the file (before the closing </menu> tag add both the 'Usual Applications' definition as well as all the move instructions. Be sure to edit the move entry for 'Internet' and change 'Internet' to 'Network' as that is what the internal name of the category really is.

   <Menu>
   <Name>Usual Applications</Name>
   <Directory>usual-apps.directory</Directory>
   <!-- This is the target of <Move> at the end ... -->
   </Menu>

   <!-- Move default top-level menus one level deeper -->
   <Move>
   <Old>Accessories</Old>
   <New>Usual Applications/Accessories</New>
   </Move>
   ...
   <Move>
   <Old>Hamradio</Old>
   <New>Usual Applications/Hamradio</New>
   </Move>

Once fixed the 'Usual applications' icon will be missing. This can be resolved by removing the .png extension for the icon entry in /usr/share/desktop-directories/usual-apps.directory.