Adding Metadata to RSS Feeds

I have a block of information that comes from custom fields. I display it with the following code on the pages themselves… how can I get this same information appended to the RSS feed (all feeds would be even better) for each item?

Display Code

if (get_post_meta($post->ID, author, True)) {
    if (get_post_meta($post->ID, authorlink, True)) {
    echo  '<p>';
     echo  '<a>ID, authorlink, True) . '">';
    echo  get_post_meta($post->ID, author, True);
    echo  echo '</a>';
    }
else {
    echo  get_post_meta($post->ID, author, True);
    echo  '';
}
}