jquery append before final element

I have html structured like so.

<div id='container'>
  <div class='item'> ... </div>
  <div class='item'> ... </div>
  <div class='item'> ... </div>
  ...
  <div id='item_final'><input type="button" id='addOne'>...</div>
</div>

and what I am trying to do it add another item to the container class before the item_final div. The items are dynamic, so the number of them is unkown.