Getting quote item data in abstract class

Question

I'm creating an abstract class that is extending Mage_Payment_Model_Method_Abstract.

When I run

$quote = Mage::getSingleton('checkout/session')->getQuote();
$cartItems = $quote->getAllVisibleItems();

foreach ($cartItems as $item) {
    Mage::log($item->getSku(),null,'test.log',true);
}

I get nothing in the logs about this. How can I get access to the items?

Update

Thanks to Amit's answer below I was able to find out how to get the sku for the order

$orders = Mage::getModel('sales/order_collection');


foreach($orders as $order){
    $items = $order->getAllVisibleItems();
    foreach($items as $item){
        $sku = $item->getSku();
    }
}

Answer 1

As Mage::getSingleton('checkout/session')->getQuote() using it working

on frontend

but it does not work on backend.

For backend magento use different model

 Mage::getSingleton('adminhtml/session_quote')-.

Better solution is below:

$paymentInfo = $this->getInfoInstance();

if ($paymentInfo instanceof Mage_Sales_Model_Order_Payment) {
        // used  for order object
     } else {
         $Quote = $paymentInfo->getQuote();
    // put your code  here  
        $Quote = $quote->getAllVisibleItems();
        foreach ($cartItems as $item) {
         Mage::log($item->getSku(),null,'test.log',true);
        }
     }