I'll add my list - it duplicates some stuff here already, but this in its entirety is what we pack in suitcases for flying. This list does NOT include standard stuff like clothes, makeup, hair products, things like that.
Of course, there are some things others have posted that we personally don't care about, like swim spray, so this certainly isn't a complete list for everyone, but it is for us. We also don't plan to do laundry on the trip.
We usually do one grocery stop the first night via bus down Harbor to Target, for other things we want (mostly food/beverages/snacks).
And since we've only gone in the summer, this is our summer list!
Swimwear, Water shoes, Swim diapers, Life Vests
Extra Clothes (in case you get soaked on Splash, or need to change mid-day for any reason)
Walking Shoes
Cooling towels and hats
Glasses/Contacts/Contact Solution/Eye Drops
Prescription Medications
Medical devices/items, such as retainer, sleep mouthguard, knee braces, whatever you personally need
Tylenol, Ibuprofen
Moleskin, Liquid Bandage, Bandaids, Gold Bond Friction Defense/Bactroban (aka Neosporin)/Hydrocortizone
Sunscreen, Aloe, Sunglasses
Cameras, all Batteries, Memory Cards, Card Reader for them
Phone chargers
Laptop/Kid's Video Games/Portable DVD Player/AvOut cords
Chargers/Batteries/Headphones for above
Sitting Blanket
Emergency Ponchos (World of Color, for kids on water rides)
2 Large Garbage Bags (For all dirty clothes)
Big pile of Ziploc Bags - Quart and Gallon - These always get used in unintended ways
Favorite Toys
Travel reading material
Kids Cups
A Power strip - always bring one when staying in hotel
Nightlights
Disney books
Ground Coffee and Filters - Hotel stuff usually makes 1/2 cup
Snacks + small soft-sided cooler
Autograph book + pens
Quarters/Pennies for pressed pennies
Cash
Printed copy of all vouches -
Disneyland ticket vouchers/Photopass+/Shuttle
Printed copy of all Confirmations - Hotel, Car rental, etc
Lastly, we bring the kid's birth certificates and our passports (alternate ID for us). I know people have different feelings about this. We keep them stowed away the entire trip, they are just in case of emergency or lost main ID. Fortunately, we've never had to use them.