Don't book any excursions, just go ashore and speak to a taxi driver. They will tailor what you want for a fraction of the price. They all speak English and can't do enough for you.
When I did OV Caribbean in March, we were advised to go the desk inside the port area where you can book trips there and then for a fraction of OV price. We did this in St Lucia and had a stunning day out via boat and mini bus - very cheaply. Also when you walk out of the port gate licensed taxi drivers are there waiting for you. Just ask them the best trip they offer and a price. If you have some idea of where you wish to go they will take you - stop any time for you to take pictures - a drink - they are really lovely people you feel your trip was money well spent. Most of the ports in the Caribbean are purpose built- shops, shore booking desk, cafe - music - and so relaxed. The Caribbean is no doubt the best cruise I have ever taken as I have now done most of the Med ports and nothing compares to the Caribbean.
I am glad i read this as i am also going 19 dec i found it hard to find much that my 5 year old. i hear there is quite a few things planed for christmas day.