I haven't done the flight to Orlando with my kids, but we've done longer ones to the west coast and Texas quite a few times.
Expensive but great suggestion: iPod Touch. Amazing for entertaining little ones and it takes up very little space.
Wrapping some little presents gives the fun of unwrapping and makes them more exciting, but I'mn a little wary of this with security checks now. My parents used to do it with us when we were younger.
Stickers! They seem to keep my kids entertained way longer than I understand. Play-dough or plasticine. Those pens with the caps that can't get lost are good. Don't forget paper and/or colouring books. A little car or two can "drive" all around the tray table and seat area without a little one needing to get up.
Don't be afraid of noisy toys. Things like those books that make noise when you press a button or equally noisy toys won't be heard by neighbours over the plane noise but will give her something to do that doesn't have to involve you. I love reading stories to my kids, but after more than 2 hours of it straight I am so done. Baby "laptops" can be good too.
They make some smaller headphones she might prefer. My daughter hates the ones that fall off her head because they are made for adults.
Sounds obvious, but don't forget any cuddly toy or blanket she sleeps with. It can make the difference in whether she'll sleep on the plane.
My kids like the little pillows made by the Trunki people when they have to sleep in a seat.
From a very practical standpoint, bring more nappies, clothes, wipes and snacks than you think you need, ensuring you have a change of top for the adults too. My husband laughed at me for insisting on this on our last flight in August, but wasn't laughing after my 4 year old was sick over and over. Having fresh clothes for him and for me made the flight way less awful.
I always pack a little more than we actually need on a flight, but I'd prefer to have toys they didn't use than ages of fussing because they are bored. Anything that is a surprise that doesn't get used on the flight over is kept for the flight back. My daughter does not sleep on night flights, so I have to have a lot of entertainment for her. Last time we were in California, we spent the entire day at
Disneyland and had a 9 pm flight home. She did not sleep a wink until we got in the car to drive home, at which point she promptly fell asleep. I could have screamed.
You will survive it, and the flight home too.