I started planning (and setting aside items) for my June holiday as soon as I returned from the one over Christmas. I even went shopping and picked up a few things that I didn't want to be without on the next trip.
During our last visit, we learned the hard way that not all resorts have First Aid stations and the gift shops have very little to offer unless a standard adhesive bandage will do. Needless to say, I have already purchased new boxes/tubes of (though hope not to need) telfa pads, neosporin plus, etc. and have it safely tucked away.
About a month before we leave, I experiment with travel size items/bottles to know how much I really need of certain items (such as shampoo and conditioner) so that I don't run out too soon but also don't waste room in the luggage that is becoming more costly to take each trip. The goal is to only have enough for an extra day or two.
Additionally, we are taking one of my daughter's friends along on this trip and as she has never been to the world before, I must have a complete list created so that she doesn't end up with the wrong items (such as a bikini rather than a one piece swimsuit for the water park).