Hi Jonathan!
We always wear a backpack around the park when we visit Walt Disney World and what we find works best for us is simply place the backpack on the ground between our legs while on an attraction. Some of the experience, like
Soarin', allow you to place your backpack in a special location in the middle of the aisle so you don't have to wear it during the experience. On boat or large car attractions, such as
It's a Small World or The Great Movie Ride, you can simply place the backpack on the ground and it fits well.
You can also consider renting a
locker if you will be going on a lot of attractions and you don't want to have to worry about storing, wearing or lugging your backpack with you. I also like to use a small Camelbak, which serves as providing the family with water, as well as holding my essentials. This is small enough that I can wear it the entire time, even when on the attractions.
I hope you have a magical vacation!
Magically,
Stacy