Here's a list that I've been compiling. There was another thread along the same theme during the summer.
AAA Card
A giant bag to put dirty laundry in for storage and to take to the laundry room
All of my monthly/weekly magazines from the preceding month (I save them for the trip)
Aloe vera
Anbesol (for toothaches)
Anti-bacterial gel
Band Aids
Batteries
Bee sting kill wipes
Blister shield
Breathe right strips and throat spray (saves nights sometimes)
Camera & camcorder (don’t forget tapes/memory chips, film)
Change of clothes (put in ziplock bag in backpack)
Change of socks for all (ziplock bag in backpack)
Change purse for basic necessities and leave the big wallet at home
Chapstick
Clear Backpack (easy for security checks)
Clothes pins
Copies of flight info, driver’s license, credit card, park tickets, reservations (keep originals and copies separate)
Dryer sheets (in case you do laundry)
Empty collapsible suitcase for bringing home goodies
Extension cord (power strip)
Extra batteries
Extra contact lenses/solution/glasses
Extra credit card
Extra hats to replace the lost ones
Extra pair of shoelaces for sneakers (someone's always breaks)
Feminine hygiene products (just in case)
Film canisters or M&M minis candy containers (for pressed penny machines)
Film
First aid cream
First aid kit
Green tea bags (place in water bottle - instant flavor!)
Hand Sanitizer
Hand warmer packets (in case you stay to watch fireworks)
ID card (laminated) for your child's pocket (put child’s name, your name, your cell #)
If park tickets are pre-purchased a photo copy of the back of them in case they are lost
In a small ziplock bags children's Tylenol, generic benadryl, a spoon measuring thing for the meds (for taking into the parks)
Index cards with you plan for each day (be sure to include you ADR confirmation numbers, EMH, etc.)
Insect repellant wipes
Insurance, maps, tips, etc. (carry in tote bag with you on plane)
Medicine (Advil, Aleve for the joints, Antacid tablets, Aspirin, Cold Medicine, Cough syrup, Headache medicine)
Memory chip for camera
Mesh laundry bag
Mini-fans w/mister (for summer)
Moleskin or other products for blisters
Mosquito wipes (for summer)
Motion sickness medicine
Neosporin Antibiotic ointment
Nightlight
Over-the-counter temporary filling gummy stuff (from drug store)
Pepto-Bismol (or Imodium)
Permanent marker (can be used to write child’s name, your name, your cell # on child’s back or for autograph books)
Plastic cups or Paper bathroom cups (don't trust those glasses by sink)
Plastic ID for security and keeping tickets in
Ponchos
Power strip to plug in the laptop, digi camera and 2 cell phone chargers in one easy location.
Powdered laundry soap (get from local Laundromat)
Pre-bought autograph books (get them at your local
Disney store and Velcro a BIG (i.e., THICK pen for the characters)
Rechargeable batteries and charger
Retractable Sharpie for the Autograph book (with a quart sized zip lock to keep them both in so they stay dry!)
Roll of quarters and some singles for any tolls
Room air fresheners
Safety pins
Scissors
Sleep aids
Small fans
Small flashlight (in case accident happens at night)
Small screwdriver kit for eyeglasses, sunglasses and putting batteries in the new toys
Small sewing kit that has needle, thread, scissors, a button, and safety pins
Small umbrella at the dollar store
Sterlite plastic containers (one is food items, one is medical items)
Store shoe bag (from $1 store for hanging over back of bathroom door)
Suction cup hooks for wet clothes (to hang in the shower)
Sunscreen
Superglue (for broken nails)
Swimmers ear medicine
Tension shower curtain rod (mount directly over the bathtub for dripping wet swim suits)
Toothbrush & toothbrush holder (from $1 store that way you can leave them behind, if desired)
Travel size deodorant
Tweezers
Vaseline
Walkie talkie
Washcloths
Wipes(individual travel size)
Ziplock bags into the parks (for cell phones and cameras when riding the really wet rides)(of all sizes, snack to gallon, for various uses)
1/2 to 1 inch binder w/tabs for itinerary, tickets, park info, emergency numbers of doctors
Like I said, I've been keeping this for awhile. Whenever I run into a new idea, like the inflatable air pillow, I'll put it on the list. 
