I have several Anker battery chargers in different capacities. This one is great for park usage.
https://us.anker.com/collections/portable-power/products/a1231-2
The nice thing is it's PD capable, It'll get you +50% charge in about 30 minutes if you have a newer PD (18w) capable phone. I plug my phone in to it on Small World, Pirates, or Living with the land, and it'll charge +25% in the time it takes to ride. (~15 min). It's got plenty of capacity as well. It'll charge an iPhone at least twice, so it has enough juice to keep mine and my wife's phone charged all day