Comfy shoes for the little ones that walk. Bathing suit Hat Colouring books, puzzle books, coloured pencils - no crayons - they will melt For the older kids - a disposable camera so they can take their own pics
I'd have to say the easy going flexible attitude is number one, but that goes for everyone, not just those with kids!
We usually buy glow sticks in bulk on line (Cheap) and then let our little one give them out to others. She loves them and has fun giving them away as well. Other small toys, especially the glow in the dark/light up ones are awesome at night. Allows you to keep an eye on them as well let others who might not be looking that low to be careful.
Misters, like the battery fan/spray bottles are good, as well as something to provide some shade: Umbrellas, small kids tent, tarp or even a sheet. TN sun can be brutal without some shade. Meals are sometimes hard to arrange, so we snack alot thought out the day.
Of course a good pair of dancing shoes or some hard summer feet are required along with a decent first aid kit. Amazing how much a bandaid can help.
If you need 362 detailed reasons on why you should bring the wagon, I will be more than happy to share. We should have a whole seperate thread on the wagon!!! The wagon is your personal savior of the festival weekend. Don't leave home without it.