You can add a drawer to a panel in the following ways:
From the panel popup menu
Right-click on any vacant space on the panel, then choose Add to Panel ▸ Drawer.
From any menu
You can add a menu as a drawer object to a panel.
To add a menu as a drawer to a panel, open the menu from the panel. Right-click on any launcher in the menu, then choose Entire menu ▸ Add this as drawer to panel.