Giant McDonald's!! Where is this at? I love seeing odd places, and how awesome would it be to say "I've been to the giant McDonald's" also I do feel like I might be a little overly excited about this, but I think I'm okay with that.
If the idea of giant McD's gets you excited, then you'll also love Orange World on the 192 side of WDW. Citrus season is mostly Dec-April, so the fruit is best in those months, but the giant orange stand is there year round.
I also suggest eating off WDW property that day if you want better quality food at a lower price. The area has tons of options. Just about every chain and many non-chain options, too. Some of the places on I-Drive aren't that great, but many other spots are great.
We also sometimes use arrival day to buy a few groceries, sunscreen, or water. If you are flying and would pay luggage fees, a stop can be worthwhile.
Another possibility, if you have a whole week at WDW would be to visit Citywalk at Universal. Though the new Disney Springs has many more shops than old DTD used to have. It has changed a ton.
As another person said, many fine beaches are also relatively close. On the Atlantic side, Daytona is only about an hour east of WDW, while Tampa is only 90 minutes to the west (though actually getting ON Clearwater beach takes more like 2.5 hours with traffic/parking.)
Honeymoon Island is amazing near Tampa. If you like waves, go to the Atlantic beaches. If you like seashells, visit one of the quieter beaches on the Gulf Coast. Indian Rocks is a great beach for shells, easy parking, a bathhouse, and relatively easy traffic. All of I-4 has a fair bit of traffic, but the causeways of Tampa are kind of neat in themselves.
Between Tampa and Daytona there are at lest a 1,000 things to see/do.
When last we did an airboat ride, we went all the way to Everglades Park/Big Cyprus area (3-4hours drive from WDW), but there are airboat rides much closer to WDW.