Get ID of a page containing secondary loop in content

As others figured already out: If you have third party plugins with custom queries, you’ll have a bad day!

One solution might be caching your results.

Template (e.g.: page.php)

while (have_posts()): the_post();
    global $my_cached_data;
    $post_id = get_the_ID();
    /* 
     * If you have single meta keys, this array_map function 
     * makes them easy to access; otherwise just use:
     *
     * $my_cached_data[$post_id] = get_post_meta( $post_id) 
     */
    $my_cached_data[$post_id] = array_map( 
        function( $a )
        { 
            return $a[0]; 
        }, 
        get_post_meta( $post_id) 
    );
endwhile;

footer.php

global $my_cached_data;
echo "<pre>".print_r($my_cached_data, true)."</pre>";

Possible Result (with Page ID 2 and 15 having the same post meta data)

array(2) {
  [2]=>
  array(2) {
        ["meta_key"]=>
    string(10) "meta_value"
        ["another_key"]=>
    string(10) "meta_value"
  }
  [15]=>
  array(2) {
        ["meta_key"]=>
    string(10) "meta_value"
        ["another_key"]=>
    string(10) "meta_value"
  }
}