We just went in October and I packed everything imaginable!
Things I packed that I didn't need:
Clothes pins
Extra baby wipes (for dirty hands, stroller handle wipe downs, etc.)- I only used one pack and gifted an unopened to one when we left
Clorox wipes- I packed a huge roll in a ziplock and a travel one probably would have sufficed.
Laundry stuff- who wants to do laundry on vacation? Not me! And we packed plenty so we didn't need to.
Glo Sticks (I kept forgetting to bring them along to the parks!)
Things I am happy we had:
Baby wipes- one pack was great to have and I'm glad we had it- even shared with someone else's messy child at the parade!

Water- I ordered it from Garden Grocer (2 30-packs) and I am SO happy I did!
Kool aid and Crystal Lite water flavoring drops. Put it in your bag with your water bottles for a little added flavor!
Snacks- trail mix was the best! Good to eat any time of day! We also brought microwave popcorn, fruit snacks, granola bars, and cereal bars.
Plastic bottle of alcohol- It was nice to add to enjoy a drink by the pool or after a long day at the park
Swimming googles
Unique scarf to tie on my stroller handle- made it easier to find in the sea of strollers.
Backpacks- we brought 2 each day with waters, snacks, wipes, Advil, bandaids, extra clothes- just in case items.
Glad I had bandaids and Advil.
Nail clippers
We needed children's tylenol one day at the park and didn't bring ours along so we went to the aid station and they gave us some. That was really nice!
Another thing that was GREAT is that our kids saved up their own spending money over the year and we gave them each $60 extra and we told them that was IT for souvineers. They were so much more thoughtful about what they purchased and it really cut down on "the gimmies".
Have fun!!
ETA: Definitely bring gum if you like to have it. We brought Memo Books and Sharpies for autographs. And ziplock baggies! I brought a bunch of sandwich size and gallon size ones.