Extract array from custom field

This is mostly pure PHP, but you need to implode the array.

add_shortcode('bundled_ids','bundled_ids_func');
function bundled_ids_func() {    
    $meta_values = get_post_meta( get_the_ID() , '_bundled_ids', true );  
    if (!empty($meta_values)) {
      $mydata = implode(',',$meta_values); // add this line
      return $mydata;
    }
}