Hi Dena,
I am pleased to inform you that you can certainly
bring a backpack cooler with food and/or drinks into the parks with you. Certain items are not allowed, such as glass containers and alcoholic beverages, but otherwise, you are welcome to fill your backpack with items you will need throughout the day. You'll want to stay away from loose ice so I recommend packing reusable ice packs or sealed bags that you can put ice in to use as an ice pack.
When I arrive at a Disney Resort, one of the first things I do is place an Instacart order containing snacks and plenty of water bottles. I load up the refrigerator in my room with the water bottles so they are ready to go in the morning when I'm ready to head out to the parks. If I'm lucky, the refrigerator will have a small freezer included which works out well as I can pack a couple of frozen water bottles to double as an ice pack.
As you probably know, it is very important to stay hydrated, especially in the summer months at Walt Disney World, so I'd also like to mention that you can request complimentary cups of ice water at quick-service restaurants. Additionally, many of these locations will have a water station set up, especially on warmer days. I was pleasantly surprised when I stopped by
Dockside Diner in Disney's Hollywood Studios recently and found a nice water station set up that I could enjoy as I waited for my order. It was so refreshing and appreciated.
Enjoy your vacation, Dena. I hope it is truly magical!
Diane