Hey, howdy, hey, Rob! Thanks for bringing your question to planDisney. You must be so excited about your trip this week!
In my experience, I have been able to take a small-medium backpack on attractions with me. Many attractions have a netted pouch in which to place your personal belongings, or a small hook to secure your bag. I have also kept my backpack on the floor of the attraction vehicle and looped the handle tightly around my knee for safekeeping. The only attraction I can think of where I had nowhere to keep my backpack with me is
Soarin’ Around The World – the Cast Members have an area you can leave your backpack and then pick it up immediately after the ride is over. (By the way, this attraction is temporarily transformed back to
Soarin' Over California until April 26, as part of the
Disney California Adventure Food & Wine Festival!)
Keep in mind there is a size restriction on bags/backpacks you can bring into the parks. On the Disneyland Resort website, you’ll find a list of
prohibited items, which specifies the size restrictions on bags and backpacks – I’d recommend having a look.
There are
lockers available for rent, which are useful if you want to store things like jackets or other items you don't need throughout the day, so you can carry a smaller backpack around the parks. There are lockers inside both parks as well as outside the Disneyland Park entrance. The prices of locker rentals range from $7-15/day, depending on locker size (prices subject to change.)
All in all, I would say a reasonably sized backpack should be fine to take aboard attractions with you. The smaller the better.
Hope this information is helpful. Wishing you a thrilling and magical vacation!
Kamini