Our group wasn't so big at 16, but we did the cat cruise together on our wedding day in the afternoon after the ceremony. That was a lot of fun.
Some of the group went golfing one day, including my DH, but I didn't golf at the time (barely do now, but I've at least hit a few balls), so I went diving with a few of the divers in our group instead.
It's tough to have too large a group try to do things together on the resort though, as they're really more geared to couples, (particularly for dinners, just so you know).
I think it's nice just to throw a few ideas out there and see who wants to do what. I made some suggestions about off-site excursions to the group well before we went. I thought who ever wanted to go can go, but no pressure. In the end we didn't do any off-site excursions.
If your whole group, or majority of them, do want to do an excursion, you may be able to book a whole bus and do your own private tour.