At least 2 comfortable, well worn in pairs of shoes - trade off between pairs each day. (On a side note: I guess I'm the one person that didn't have much luck with crocs at Disney. They gave me the absolute worst blisters I have ever had on my feet after 1 day last year - made the rest of the vacation quite a challenge. I wear them all the time at home, it was only at the parks that I had this problem. I think the little nubs on the bottom of the crocs were the culprits.)
As far as clothes go, I only pack 1 outfit per day, with just 1 or 2 extra outfits. I find that changing clothes doesn't really help me much: once I step outside again into the heat, the new clothes are just as miserable as the old clothes within 5 minutes, so what's the point. And before anyone says it - I use a good deodorant, so no, I don't stink!
And I bring lots of extra underwear, so that can at least be changed after mid-afternoon swims, etc.
Other necessary items: bug spray or wipes (don't always need it, but when you do, you REALLY need it!), moleskin for any blisters that pop up (see the note on the crocs above - this saved me last vacation!), camera/extra batteries/extra memory card/charger, pain reliever (advil, tylenol, etc.), allergy medicine, small bottle of dishwashing liquid (for reusable mugs).
And the most important thing - a credit card with a really high limit! :lookaroun That one will take care of anything else I forget!