I grew up in Central Florida, and even worked for The Mouse during college I've got so many happy memories of that place, and I hope you will come away with the same!
I have pretty strong feet, I usually wear ballet flats, or dance sneakers, which are lightweight, flexible, and give the arch of the foot super-support - and there are some really cute ones out there that don't scream 'TOURIST!'.
From April-Novemberish, I usually wear shorts, and a thin t-shirt that breathes. If I'm there when the temperture reaches a numbing 70 degrees, I wear long stretchy sports-pants, and layer long-sleeve fitted tissue-tees with tanks, topped with a cute sporty jacket. Stuff that you can peel off if the temperature should climb.
I forego a purse for my small red canvas Roxy backpack, which has travelled the world and held up remarkably well. In it I put my downscaled wallet (pared down to ID, cash, credit card, health insurance info, placed towards the bottom of the bag, to discourage theft), an extra tee shirt or long-sleeve tee (Florida is hot, but the AC is freeeezing), a rain poncho (I can't think of a day at Disney or Universal that it didn't involve 'unexpected', soaking RAIN for at least 20 minutes), sunglasses, small decanted bottle of sunscreen, small brush or comb, ponytail holder, colored lip balm or gloss, travel-size deodorant, an eyeliner pencil and mascara (I like to touch-up during the day), and one of those disposable plastic toothpick/mini toothbrush combos. I also bring some first-aid stuff: a couple of advil, antihistamine, extra bandaids, pepto-bismol tablets. And a camera!
I don't usually wear jewelry, except for some fun earrings.
My mom always brings snacks, and we always laugh at her, until we're stuck in line somewhere and STARVING. Then we flatter her shamelessly and she taunts us, and then she hands around the Kit Kat miniatures, and everybody is happy. Sticky, chocolatey, and happy.
I realize this sounds high maintenance, but for a 12-14 hour day of walking around in temperatures that can go from 65 in the AC, to 100 with the heat index, all in one visit, this usually keeps me feeling fresh and energetic through the day.
I also realize that this sounds like quite a lot to carry around, but it doesn't weigh a lot, I always end up using pretty much everything I bring (except, if I've been good, the credit card!), and it's cheaper than having to buy advil or bandaids, or a poncho inside the park.
Have a wonderful trip!