We also did parasailing without booking, almost the same price as if booked on the ship, but again, we only had one hour or two and had to do that close to the port, which would be more expensive. In Jamaica, we visited a park with beach and a fall, costing per person $10 for the shuttle bus and $16 for the entrance. I found out later it would have been somewhere around $70 if booked a similar tour on the ship. One advance for booking tour through the ship is that if it is a long trip, like 6-hour trip in Cozemel to see the Mayan ruin, and if you are late, the ship will be waiting for you. But it didn't apply to us since we couldn't go so far.
So I think you can either book online or arrange a trip on spot. There will be a lot of local guides asking for the business, and usually it is cheaper than booking on the ship. Either way, you won't miss anything as there is a lot to do.
So I think you can either book online or arrange a trip on spot. There will be a lot of local guides asking for the business, and usually it is cheaper than booking on the ship. Either way, you won't miss anything as there is a lot to do.