The Quick bar is a user defined tool bar. All HTML tool bar buttons can be added to the Quick bar by simply right-clicking the button and selecting Add to quickbar.
And automagically you will see the element in the Quick bar:
Note that you cannot add a pop up menu. Thus, if the item you want to add is inside a pop up menu (as is the code tag located in the Context formatting pop up menu of the Fonts tool bar), you have to first click on the pop up menu to display its contents, then to right click on the desired element to insert it in the Quick bar.
If you want to remove items from the Quick bar, right-click them and select Remove from Quick bar.
You can also change the location of an element in the Quick bar. To do so, right-click the element and select Shift left or Shift Right as desired. The element will be moved to the left or to the right of its neighborough. Notice that this is not a drag and drop action; you may have to repeat the process if you want to move the element farther.