Hi, Suzanne!
Thanks for stopping by and visiting with the Disney Parks Moms Panel!
Yes,
backpacks are allowed on the attractions. Most of the attractions have a small area just at your feet to place your bag. To securely hold my backpack, I always step through one of the straps and pull up the bag up toward my lap once I'm seated on the attraction. This is always helpful for faster attractions such as
Rock 'N' Roller Coaster Starring Aerosmith. Some attractions, such as
Avatar Flight of Passage have small cubbies just behind the ride vehicle to store your belongings, and Soarin' has compartments under each seat. If your backpack is filled with all of your must-haves for the day, these compartments will hold your backpack with no problems!
Also,
lockers are available to rent in each park. Small lockers at $7/day and large lockers are $9/day. Both require a $5 refundable deposit. Epcot and Disney's Hollywood Studios have single use lockers for either $1.00 or $.50 depending on the size.
Enjoy your time "backpacking" through Walt Disney World! This will be the most magical "backpacking" time of your life!
Korliss