Pre-populating Post Types with Default Content

The following snippet lets you add default content automatically to every new post of a given post type. Add to functions.php:

<?php
////////////////////////////////////////////////////////////////////////////////////
// This auto populates post types and posts.
///////////////////////////////////////////////////////////////////////////////////


function my_editor_content( $content ) {

	global $post_type;

	switch( $post_type ) {
		case 'your_post_type_here': //auto populate
			$content = 'The content you want to pre-populate the post type with.';
			break;
	}

	return $content;
}
add_filter( 'default_content', 'my_editor_content' );

For more on custom post types, see How to Create Custom Post Types.