I agree with the previous poster about dressing in layers.
We go backpacking, so are used to packing light. For the flight/travel day we wear long pants, a short sleeved shirt, AND our layering clothes: a long sleeved shirt, a sweatshirt and a zip up jacket. For Disney we pack 4 outfits and then use the layering clothes as needed.
At Disney we do laundry once every 4 days (on our rest days).

I bring small gel detergent packs called Dropps. They take up very little room and work fine. I have seen them at Linens and Things and Target.
For actual packing we roll all of our clothes, placing each outfit in a zip lock back (removing any extra air). This way they take up as little space as possible

. We set aside our clothes to pack way in advance. However, we don't pack our bags until the night before or the morning of travel, so we aren't "the wrinkled family" the first 4 days there.
(For backpacking we just pack one outfit for each day and don't care about wrinkles

.)