What are the must do's?

Offsite:
I have Dunns River Falls on our list. I saw a video about the Dunns River Falls tour. Is it a hard climb up?
I also want to do Horseback Riding.... posted a seperate thread on that. Know that's an additional cost.
Hubby is interested in ziplining. Thoughts? Also, additional cost.
Thought about the shopping tour but heard mixed reviews. Thoughts?
Any other suggestions?

Resort Activities:
We want to do the snorkeling trip for sure. Do the tours book up quickly? Do they have multiple times slots during the day?
We were also thinking about Glassbottom Boat but assuming it's same boat they take for snorkeling so not sure if it's worth it.
How about the other water sports.... options?
Also thinking about taking the free tennis lesson... worth it?
Any other land activities we should do?

TIA