to answer your question about a float thing - I got one that is mesh in the middle, with an inflatable rim. It takes absolutely no space in the suitcase because it packs flat, and is wonderful to float on because your butt is actually in the water when you use it! You may have a tough time finding one at this time of year - I got mine last summer in
Walmart.
As the pp said, guys need to dress in long pants for for dinner - women are a little more relaxed. I've seen jeans and fancy top in the restaurants for women, and shorts in the buffet at dinner also. You don't have to be dressy-dressy, just not sloppy. You can literally wear your bathing suit and a cover up to the beachside restaurant for lunch.
The only excursion I went on was horseback riding on the beach. I'd read to book something with Rancho Pat's, supposedly the best. They pick you up at the hotel and the stables are literally 5 or 10 minutes away. The ride was a little hairy at first as we had to ride through a hotel construction site

(and I mean, right through it!) but, once we were clear of that, we galloped down virgin beach with the waves crashing beside us! Awesome!!! I can't recall exactly how much - I think it was like $40. There are other stables, but I believe they are in the jungle rather than the beach. The guides were great, they would take our cameras, gallop up ahead of us, then stop and take our pictures as we galloped along! naturally, they were kind of hoping for a nice tip afterwards
I think I've usually gone through about $50-$60 in $1's - I usually leave $2 for housekeeping every day, a little extra if I leave a note for something additional; I don't always tip at the buffet, really depends on the service; always tip the a-la-cartes and we've always used a "$1 per head" rule. Also, doesn't hurt to make a habit of choosing a table in the same area each day for lunch. Your server will get to know you, and if you tip a $1 here and there, they'll treat you right
The shows are...umm....well...let's just say, my sister fell asleep in the middle of one! LOL but, the one you have to take in is the Michael Jackson impersonator. He's really quite good! To be honest, we usually skip the shows now, they're quite predictable and generally a little on the lame side. After a full day in the heat, it was all we could do to scrape ourselves off the beach at 5:30 pm, clean-up and pre-dinner drink; dinner; after-dinner nighcap; and then c-r-a-w-l-e-d back to our rooms for a good nights rest! It's amazing just how tiring it can be to sit in the sun all day!!
If you're interested, you can see some of the photos I've posted here:
http://ceejanerun.smugmug.com/Personal Photos/661134