functions.php

add_filter( 'wp_nav_menu_items', 'theme_menu_extras', 10, 2 );
function theme_menu_extras( $menu, $args ) {

	if ( 'secondary' !== $args->theme_location )
		return $menu;

	//* Uncomment this block to add a search form to the navigation menu
	/*
	ob_start();
	get_search_form();
	$search = ob_get_clean();
	$menu  .= '<li class="right search">' . $search . '</li>';
	*/

	//* Uncomment this block to add the date to the navigation menu
	/*
	$menu .= '<li class="right date">' . date_i18n( get_option( 'date_format' ) ) . '</li>';
	*/

	return $menu;

}