Function to get all custom fields within the $post global

get_all_post_custom_fields.php

<?php
function get_all_post_custom_fields( $posts ) {
    for ( $i = 0; $i < count($posts); $i++ ) {
        $custom_fields = get_post_custom( $posts[$i]->ID );
        $posts[$i]->custom_fields = $custom_fields;
    }
    return $posts;
}
add_filter( 'the_posts', 'get_all_post_custom_fields' );