Hi Christine!
Thank you for bringing your question to the Disney Parks Moms Panel!
Backpacks can be a lifesaver when you're spending the day at a
Walt Disney World theme park, especially if you have young children. I love having one for snacks, water bottles, sunscreen, wet wipes, cameras and so much more!
You are allowed to bring your backpack onto the theme park rides. I do it frequently. But, it will depend on just how big and full your backpack is. Cast Members do have the right to request that you leave oversized bags that don't safely fit into the ride vehicle with them.
Here is a
link to Walt Disney World park rules for you to read through. Please note that all bags will be searched before entering any of the parks.
I hope this helps! Please let me know if you have any other questions.