One great tip is to pack the kids whole outfit, including hair ribbon, matching sox into 1 gallon zip lock bags for each day, each child, then even DDad can dress the kids and get all the matching pieces dressed on the child.
So add 1 gallon zip lock bags to your list.
That's a great tip I've used for a few year now, especially with my dd who has so many accessories with each outfit. It makes life a little more efficient especially when trying to rush everyone out the door for ee/mm. Definitely add assorted size ziploc bags to your list. I don't think you can have too many ziploc bags; sandwhich size, quart size, gallon size.
My kids swear by crocs. They've worn them for the past 4 DL trips and live it in during the summer. I've yet to be adventurous enough to wear them.
When packing clothing, think layers. Early mornings and evenings may be bit chilly (Sweatshirts, light sweaters and light jackest) but afternoons can get pretty warm. Dd loves his pants that zip off into shorts. Dd loves dresses & skirts so we put her in tights and later remove them when it gets warmer."Quick dry" clothing also is a must for our family since we love wet rides like splash mountain and grizzly river run. Ds sometimes just wears his swim trunks if we plan to do reride a wet ride several times in one day.
I notices that you have 3 girls, if they have princess costumes at home bring those too. DD loves to dress up like a princess when we go to DL. Buying them at the park can get quite spendy as each princess dress is $50+. I picked some up at the
disney store and disneyshopping when they have their sales. If your son has a costume too, bring it along.
Sunscreen, hats, purell, wipies, and tissue. Oh yeah, I also carry a tide stick pen in my purse, especially with my kids. It just comes in handy with those little spills on clothes.
Don't forget to pack something to keep your kids occupied in lines. Our kids bring their ipods, which I hold in my purse when not in use, and it works wonders. We download audiobooks on it for them as well as disney movies and tv shows. The electronic game 20 Questions is also one of our family favorites.
Also, don't forget cold/fever medicine for children. Dd got sick on one of our trips. She had a fever on the 4th day of our 5 day tip. We thought she had the flu. Luckily we had a rental car and could drive to the store and pick up a thermometer and medicine. We ended up taking her to the doctor's when we got home and she was diagnosed with walking pneumonia.
Whew, that's about all i can think of.
My BFF swears by hers. So, we are bringing our Crocs, but also comfy standbys we can count on!
But I think you should pack a sweatshirt because nights at the park can get really cold. 
