I think you would miss your 24L... When I went on my cruise, it seemed like everything on the ship was BIG, and my WA got a lot of use... Same with Cancun - if you take any day trips and visit the ruins or tidal fish ponds - you will want the WA... The skies and the clouds are vibrant - bring a CPL...
I will definitely bring my CPL's.
My A1000 IS sucks. It doesn't even have manual controls or Raw shooting. Maybe a used s95 or s100 or G12 to use with my 580EX II?
Ditto on the 24L. I would strongly suggest you go light. Just the SLR, 24L + 24-105 and maybe flash. Also, the 16-35L is my favorite lens. If I could only have two lenses, the 16-35 would probably be one of them. You still have to take the other stuff, CPL, maybe amber gel for flash, cleaning stuff, batteries, media, chargers, etc. My point is that the SLR creates a whole giant world of extra stuff to carry. I think you would likely be happy with just a G12. Or G12 during the day and maybe the 5D3+24L at night. It's a lot to carry around. I hope you have a Black Rapid strap or something to keep it out of your way.
Remember, the more you take, the more is left in your cabin, could be stolen, etc.
Also, if you plan to go swimming, do beach trips, sit by the pool, etc consider a rugged waterproof camera like the Canon D20 or a GoPro. Lots of fun, zero worry. Decent pictures, esp underwater. Try to get away from the camera a little, it is a vacation after all. Have a great time!!