We bring a collapsable closet shelf, but ours is meant for shoes. We also bring about 10 of those small plastic white baskets (you can find for about "3 for $1") The baskets fit perfectly in the show openings. Everybody gets two baskets, (Dd, 13 tomorrow, could use more!

) and there is one for other assorted items such as first aid, sewing kit, hair, another for receipts, etc. It really helps keep everything organized, and I like being able to grab my basket and head to the bathroom, or over to the desk/mirror area (with two teens, I never know when the bathroom will be available to brush my hair, etc.) This works better for us than keeping an over the door organizer in the bathroom.
I am sure that this would work for smaller outfits for younger kids (without using the baskets.)
We will also be bringing a pressure curtain rod and clip rings/sheet for our room at the Poly, as there is no divider between the sink area and the toilet area. I am actually a little surprised at that. When we stayed at the POR, we brought a shower curtain and those stick on/easy take off hooks to keep the sink area private - that worked great, but I think that there is now a curtain in that opening (they caught on!)
I bring peppermint foot lotion for the end of the day. Yum!
We will bring a small timer for the shower to help limit time spent (2 teens and Dh and I sharing 1 bathroom!)
We are bringing some Via, that Starbucks instant coffee, to add to our Nescafe. We like strong coffee, and really do not like the Nescafe.
Photocopies of fronts and backs of any Disney Gift Cards and Credit Cards that we bring. Anything important ID wise that I carry with me from the house, I will photocopy. (Backs have phone numbers and other important numbers.) Keep these in the safe.
An extra large plastic bag (Dollar Store has these) to carry with me to put my backpack in when we ride a wet ride (Kali River Rapids, etc.)
I am considering bringing binoculars.
Prior to Leaving, Other things that are helpful:
My Mil recently was in a car crash, and thankfully she is ok, but I was impressed that she carried with her in her pocket book a notebook with exactly what medications she takes/recent surgeries, her drugstore information, (prescription numbers) etc. This was invaluable to the doctors. Her medications were not in her handbag, they were in the back of the car, which had been towed - since she had the information, and I remembered to ask about them, the doctors at the hospital were able to give her prescriptions of her medications prior to sending her home with us, and since she is on a number of medications, and she was somewhat stunned, this really, really helped. There are a few medications in my family, and I will be copying down all the information into my little book and carrying it with me in the parks. Just in case.
Also important, we make sure that the person taking care of our dog has our dog's rabies certificate nearby where the sitter can see it, and we point it out to him. This has never been an issue, our dog is a sweetie pie, but you never know. We also fill out a small form approving how much we will pay for an emergency vet appointment without our knowing anything, prior to us having a conversation with our dog sitter/vet. This is so that they don't worry, and we know our dog will be taken care of immediately. I had a bad situation once pet-sitting someone's pet hamster, and I don't want to put anyone in a similar situation. The amount stated is pretty generous, but I would want to be part of a conversation about his health anyway, before major decisions were made.
Doing those last items may never be important, but they will give me peace of mind.