I understand you girls are much older than my kids, but having gone three days last week, I think I've finally gotten my DL gear whittled down to the "basics". So this is a general list, take what you need from this list (obviously, you won't need the diapers)!
Full change of clothes for each child (down to the underwear and socks)
Pajamas for each child (the clothes and the jammies are packed in individual gallon size Ziploc bags to keep any spills out and help keep them compact)
about 5 diapers for DD
diper cream (you don't get as many chances to change babies when you're in the park, so a rash is far more likely)
snacks (anything non-perishable that your kids will eat works)
at least 2 bottles of water
little toys, handheld games, deck of cards, anything to keep the kids occupied during long waits or down times (I stock up from the Dollar Stores and the dollar spot at Target, I don't let the kids play with it before hand to keep it new and exciting as long as possible. Some things I often get in doubles so they don't have to share.)
A small first aid kit (I know there's a whole first aid station at each park. But I am First Aid and CPR certified and it will help more to have a bandaid on hand when I need it then drag the whole group for a small scratch and an hours worth of forms. I found a great little kit in the travel toiletries section of Target for a couple bucks.)
Tylenol - headaches, cramps, fevers, pains, all come up at any time.
Disneyland Bag (so far just a shopping bag from the park, but DH found a little bag that might work):
Our hats - the kids and i got the pirate ear hats with our names embroidered on them, we'll get something with a brim for the spring and summer months.
Our pin lanyards - we bought the pouches to clip to them so we can keep our passes with the pins.
Autograph books with pens
Blankets - we got these great fleece blankets when we got our passes, they have a pocket that the blanket folds up into to make a pillow and a great compact size.
DL ponchos - after being unexpectedly rained on Wednesday night, we take them with us now. our two adult and two child ponchos fold up nicely into a one gallon Ziploc bag.
Camera - I dump the images from my 128mb memory card every night after we get home from the park, weather I've taken two pictures or filled the 130 spaces.
During the late spring and when I can get in during the summer, I plan on taking a pair of water shoes for each kid, I know there are a few places for the kids to just play in the water at DCA and they will love this. I'll take the ponchos out of the bag at this time.
Like I said, this is specific to me and mine. What you need to take will vary greatly.