getorderproducts.php

<?php

$order = 13;
$attribute = 'url_key';

require_once 'app/Mage.php';

Mage::app();

/** @var Mage_Sales_Model_Order $order */
$order = Mage::getModel('sales/order')->load(1);

/** @var array $itemIds */
$itemIds = Mage::getResourceModel('sales/order_item_collection')->setOrderFilter($order)->getAllIds();

/** @var Mage_Catalog_Model_Resource_Product_Collection $productCollection */
$productCollection = Mage::getResourceModel('catalog/product_collection');
$productCollection->addFieldToFilter('entity_id', array('in' => $itemIds));
$productCollection->addAttributeToSelect($attribute);

foreach ($productCollection as $product) {
    /** @var Mage_Catalog_Model_Product $product */
    echo $product->getId() . ': ' . $product->getData($attribute) . PHP_EOL;
}