Setting the post id in a cookie

I am trying to set the post id in a cookie. I am getting the “headers already sent” error if I put it in the header but when I hook it to init in functions file I can’t access the global for post_id.

function set_new_cookie() {

global $wp_query;
$post_id = $wp_query->post->ID;	

setcookie("cookie1", $post_id, time()+36000000);
}
add_action( 'init', 'set_new_cookie');
?>

Can I put this somewhere where it will work correctly?