Have not gone to WDW with a baby but did go to a theme park more local to me with a 10 month old. I saw that someone else recommended you carry an extra shirt which is a great idea. I'd also recommend you take a few extra blankets. Put them in a zippy bag. The extra shirt as well. Unexpected spills happen. Even if you don't need extra blankets because of a spill or a leaky diaper something else will come up. If nothing else you might have to park your stroller in the sun. An extra blanket over it to keep the sun from making the seat too hot can be a blessing. Learned that one the hard way.