Here's a great tip I picked up. On checkout completion, the page shows once with "Checkout Success" etc.
However, when you press F5 or refresh, you get dumped to an empty cart and have to go through the whole thing again.
But you can stop this.
Go to:
app\code\core\Mage\Checkout\controllers\OnepageController.php
and comment out line 227:
//$session->clear();
Now, next time you go through checkout, you can refresh the page as much as you like, and get all your CSS layout, xml, etc all sorted in one go.
Fantastic.
Don't forget to change it back though!!
