Look for any available excursions that cost $50 or less, and book them once onboard. No need to actually go on the excursion. At the end of the night, you'll receive the excursion credit ($50 max), and it will be refundable. This is a way of "washing) your OBC. It works great for me, but I'm only converting the $100 shareholder credit, so I only have to find two or three excursions.