How to insert content from another Custom Post type into Post?

Currently the best way I know to handle that is the Posts 2 Posts plugin:

• http://wordpress.org/extend/plugins/posts-to-posts/

Here’s an example showing how to set up the custom post types (if you already have them it’s more for other’s benefit who might be reading this) as well as the function call to p2p_register_connection_type() needed by the plugin to set up the post relationships. This can can go in your theme’s functions.php file or in a .PHP file for a plugin you might be writing:

add_action('init','event_performer_init');
function event_performer_init() {
  register_post_type('event',
    array(
      'label'           => 'Events',
      'public'          => true,
      'show_ui'         => true,
      'query_var'       => 'event',
      'rewrite'         => array('slug' => 'events'),
      'hierarchical'    => true,
      //'supports'      => array('title','editor','custom-fields'),
    )
  );
  register_post_type('performer',
    array(
      'label'           => 'Performers',
      'public'          => true,
      'show_ui'         => true,
      'query_var'       => 'performer',
      'rewrite'         => array('slug' => 'performers'),
      'hierarchical'    => true,
      //'supports'      => array('title','editor','custom-fields'),
    )
  );
  if ( function_exists('p2p_register_connection_type') )
    p2p_register_connection_type( 'event', 'performer' );

  global $wp_rewrite;
  $wp_rewrite->flush_rules(false);  // This only needs be done first time
}

Then within your theme’s template file single-event.php you can add code like the following to display information about each Band (I showed the basics here; I’ll leave for you to fill in all the details and/or to ask other more specific questions here on the WordPress Answers site such as if you need to know how to get the featured image, etc.)

<?php
  if (count($performers = p2p_get_connected($post->ID))) {
    foreach($performers as $performer_id) {
      $performer = get_post($performer_id);
      echo 'The Band: ' . apply_filters('the_title',$performer->post_title);
      echo 'Facebook Link: ' . get_post_meta($post->ID,'facebook_link',true);
    }
  }
?>