Runs when an editing page gets generated to add some content (eg. fields) to the submit box (where the publish button is shown).
$post - (WP_Post) Post object.
Below is a basic example that will add a select box right before the submit button.
<?php
add_action( 'post_submitbox_misc_actions', 'my_post_submitbox_misc_actions' );
function my_post_submitbox_misc_actions($post){
?>
<div class="misc-pub-section my-options">
<label for="my_custom_post_action">My Option</label><br />
<select id="my_custom_post_action" name="my_custom_post_action">
<option value="1">First Option goes here</option>
<option value="2">Second Option goes here</option>
</select>
</div>
<?php
}
?>
Triggered in wp-admin/includes/meta-boxes.php