Magento2 Orders – Get Order Collection and Product SKU

I need a way to get latest 100 Orders including the ordered sku(s).

This is what I tried:

use Magento\Framework\View\Element\Template;

class Orders extends Template
{
protected $_orderCollectionFactory;

public function __construct(
        \Magento\Sales\Model\ResourceModel\Order\CollectionFactory $orderCollectionFactory,        
        \Magento\Framework\View\Element\Template\Context $context,
        array $data = [])
    {
        $this->_orderCollectionFactory = $orderCollectionFactory;
        parent::__construct($context, $data);
    }
protected function _prepareLayout()
{

    // get last 100 orders
    $ordercollection =$this->_orderCollectionFactory->create()->addFieldToSelect(array('*'));
    $ordercollection->setOrder('entity_id','DESC');
    $ordercollection->setPageSize(100);
    $ordercollection->setCurPage(1);

    $this->setOrdersColl($ordercollection);
}
}

In my template file:

<?php
    $ordercollection1 = $this->getOrdersColl();

    foreach ($ordercollection1->getItems() as $order) {
        echo "<br>order: ".json_encode($order->getData());
    };
?>

Result:
The Orders are printed out individuallay as arrays, each containing order informations (as array elements).

BUT I am missing the ordered product sku or id in those order arrays.

I need to know which products were ordered.
Any help on how I can get sku of the ordered item ?

Thanks