Here are some tips that worked for us:
* pack individual kids outfits in ziplocks -- easy to select outfit in am and Dad can help kids get dressed w/o stressing about coordinating outfits. When clothes are out of ziplocks, you know they need to be laundered. As well as your outfits and some spares, you want to make sure you have at least 2 bathing suits, hats and 2 prs comfy shoes. You may also need princess dresses. It may be easier to plan on doing some laundry so you don't have to pack so many clothes (and do so much laundry when you get home!). You can pack sample sized laundry packets (in ziplocks of course so they don't leak!!).
* We always bring a small cooler bag into the parks w/a stock of drinks and familiar snacks so we do not need to get in a line for food when the need arises. It seems if you want juice, you are inevitably faced w/a crazy-long counter service line as they don't seem to sell it at the snack carts anymore.
* Start gathering what you need in a box-- I like to use a clear storage box. Diapers, swim diapers, wipes, infant tylenol, ointments, favorite snacks, suntan lotion, hand sanitizer, etc. You may end up w/a suitcase or duffle bag just for this stuff......if you are flying and have baggage restrictions, consider shipping the items to yourself at your resort.
* Diaper bag: stock w/dipes and wipes and changes of clothes, etc. Have a large ziplock packed for quick diaper changes, so that is all you have to grab when the time comes...make sure to include a changing mat/towel/blanket whatever that is large enough for your child to lay on as well as a few diapers, small pack of wipes, cream. Imperative that DH helps you w/potty breaks, or else that is all you will be doing!!!!
* Airplane: pack individual back packs for DS 4.9 and DD3..include plane activities, lots of snacks, fruit gummies (for ear pressure on take off/landing), empty sippy cups (fill after you pass thru security), bathing suit/pjs (depending on when you land). Try to have baby drink during take off/landing to avoid ear pressure too, and bring the infant tylenol in a ziplock just in case there is pain.
* We like to gate check our strollers as well, so they are right there waiting when we get off the plane. Have been many times w/o incident to strollers.
Happy planning -- your trip is almost here!!!!