There's no direct way of creating a packing slip yet - but you can use various email templates to make sure your customers have all the information they need before sending in their return.

In the email templates you can use the dynamic variables {ITEM_DETAILS} as well as {RMA_NUMBER} and {ORDER_NUMBER}.

Make sure to include these in the email to your customers and then let them print out the email and add it to the items being returned.

Your warehouse staff then has all the details on the return.