Hi there Marci!
Thanks for visiting the Disney Parks Moms Panel with your question. I'm so excited you are planning the details of your upcoming Disneyland Resort vacation. I started taking a backpack with me into the parks last year, and now I could never go back to not having one. Sometimes I feel like Mary Poppins with how much I end up storing in it: sunscreen, water bottles, sweatshirt, diapering supplies for my son, sunglasses, autograph books, phone charger, hand sanitizer, bubble wands, and souvenirs to name just a few things. I also love that I can have everything I need while keeping my hands free to take pictures and snack on some yummy Disneyland treats.
I have taken my backpack with me on every attraction, and it has been fine by my feet. If you do not want to get it wet on
Grizzly River Run in Disney California Adventure Park, you may stow it in lockers located near the entrance of this attraction for no charge while you ride. Over in Mickey's Toontown in Disneyland Park, when you ride
Gadget's Go Coaster, you will place your bag on the side of the track when you get seated in the coaster. Since there is only one set of ride vehicles, your bag will be waiting for you right next to the track when you step off the attraction.
I hope this helps, and I can't wait for you to make some magical memories at the Happiest Place on Earth.
-Jennifer