gistfile1.php

<?php

$render = array();

//Good
$render['top'] = array(
  '#type' => 'items_list',
  '#items' => array(
    array('#data' => 'lololol'),
  ),
);

$render['bottom'] = array(
  '#type' => 'custom_render',
  '#something' => 'some data',
);

//Bad

$render = array(
  '#type' => 'items_list',
  '#items' => array(
    array('#data' => 'lololol'),
  ),
);

$bottom = array(
  '#type' => 'custom_render',
  '#something' => 'some data',
);

$render['#suffix'] = render($bottom);