You can use wp_get_nav_menu_items
to grab the menu in question,
then go through the array of items to output the content
function output_landing_page_content(){
//grab the menu items in order
$menu_items = wp_get_nav_menu_items( $your_menu_id, array( 'orderby' => 'menu_order' ) );
foreach ( (array) $menu_items as $key => $menu_item ):
//get post id of linked page/post
$postid = url_to_postid( $menu_item->url );
$your_menu_linked_post = get_post( $postid );
//format content
$your_content = apply_filters('the_content', $your_menu_linked_post->post_content);
//display each page/post content however you want (add in titles, author meta or whatever)
echo $your_content;
echo '<hr />';
endforeach;
}
just place your function in the template for your landing page