I always pack the day before because I have it down to a science.....we travel alot so some things like toiletries I never unpack.
Here are some of things I shared with my DBF to get ready really early to relieve some of her stress.
-Sunscreen, lots of it. It is very expensive in the resorts & they have a very limited selection.
-Portable GPS + charger if you are renting a car
-Call Garden Grocer & put your order in
-Cell phone & camera battery chargers
-make sure all your luggage has correct tags with all your info on them
-try to mark your luggage with something that will make it stand out (especially if it's black) my DBF & I made pictures with her kids on heavy paper...they decorated the paper on one side & we put all their info and laminated them to use as luggage tags
-Pack your "busy" bags for the plane depending on the age of your kids...coloring books, gum for ears, playing cards, etc
-DVDs to use in the resort for down time or a very rainy day
-put together your umbrellas, ponchos
Just some ideas to give you a head start. Enjoy your trip!