Distros using Gnome have pretty much standardised on the main panel's appearance and content. We get three main drop-down menus: Applications, Places and System.
Customising Applications and System is straighforward, and quite intuitive (right-click on either of them, choose Edit Menus, and have a play...). However, the same cannot be said for Places. By default, the top part of it gives a direct access to user home directory and their Desktop. But if you want to add another quick-access location, you need to realise that the Places represents a shortcut to the Nautilus Bookmarks.
So, to modify the list of directories accessible via Places you need to edit file manager's Bookmarks. Open your file manager, select the Places view for the left hand-side pane, then edit it by dropping or deleting directories into it (see the screenshot).
