I recently had a client who wanted various items placed within the side columns of her site, but not within actual sideboxes. After initially playing around with tpl_main_page.php in the templates/MYTEMPLATE/common/ folder, I found a better way to do this.

You can actually create side panel features that can be controlled just like any other sidebox (Tools --> Layout Boxes Controller), but aren't actually displayed within a sidebox template.

This is particularly useful if you wish to display a SSL security seal or trust seal within a column on your website.

To create a custom side panel feature, create a new PHP file with the code below. Be sure to change CUSTOM_NAME with your own chosen name.

PHP Code:
<?php
// -----------------------------------
// MY CUSTOM SIDE PANEL ITEM
// -----------------------------------

  // test if box should be displayed
  
$show_CUSTOM_NAME true;

  if (
$show_CUSTOM_NAME  == true) {
      
?>
            
      <div align="center" style="padding:5px;">
         PLACE YOUR BOX CONTENTS HERE
      </div>
            
      <?php }
?>
Save the file as CUSTOM_NAME.php (replacing CUSTOM_NAME with your own name, providing it is consistent with the one used in the page code). Upload the file into the includes/modules/sideboxes/ folder. Then log into admin, and select Tools -> Layout Boxes Controller to manage your new feature. You can select which column to display it within, along with its sort order, just like any other module.

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P.S. My apologies if this has been discussed a thousand times before.