The related_content block is reserved for content for the right sidebar. If no related_content block is defined, then the table will automatically consume the full width of the page.

Application widgets can easily be inserted by using the <mtapp:widget> template tag. But the contents of the sidebar are left entirely up to you.

<mt:setvarblock name="related_content">
    <mtapp:widget
        id="quickfilters"
        label="Quickfilters">
      <mtapp:ListFilters>
      <ul>
        <li><a href="#somewhere">A link!</a></li>
      </ul>
    </mtapp:widget>
    <mtapp:PageActions from="my_list_id">
</mt:setvarblock>

Tip: Don't forget to include the PageActions template tag so that other developers can dock links and actions to the listing screens you create!