ну вообще массив формируется вот так:
$product_data[$key] = array(
'key' => $key,
'product_id' => $product_query->row['product_id'],
'name' => $product_query->row['name'],
'model' => $product_query->row['model'],
'shipping' => $product_query->row['shipping'],
'image' => $product_query->row['image'],
'option' => $option_data,
'download' => $download_data,
'quantity' => $quantity,
'minimum' => $product_query->row['minimum'],
'subtract' => $product_query->row['subtract'],
'stock' => $stock,
'price' => ($price + $option_price),
'total' => ($price + $option_price) * $quantity,
'tax_class_id' => $product_query->row['tax_class_id'],
'weight' => $product_query->row['weight'],
'weight_class' => $product_query->row['weight_class'],
'length' => $product_query->row['length'],
'width' => $product_query->row['width'],
'height' => $product_query->row['height'],
'length_class' => $product_query->row['length_class']
);
ну а вообще проще вывести весь массив через
echo '<pre>';
print_r($this->cart->getProducts());
echo '</pre>';заодно и посмотреть где и что выводится.