We took our son around that age and had a great time!
Misscmac has a great list, and I strongly second the food pouches, clorox wipes, hand wipes and extra ziplock bags.
In addition to all the diaper bag staples, we also took extra outfits and a sun hat and used a backpack instead of the regular diaper bag (much easier). I also divided things into separate ziplock bags, such as 2 bags each with a few teethers and links. That way they were easy to get to, and if one got dropped or thrown, the dirty one would go back into the bag and the clean one would come out. Saved time stopping to clean things.
Also a little cooler, ice packs and bottles if you are using formula (and if you are nursing, it's very easy to do there as well. The Baby Centers are great, but there are also a lot of longer darker rides and shows, like the Carousel of Progress, that are comfortable and discreet.).
And don't forget a camera!