Hi Bryce! Welcome back to planDisney! It's fantastic to have you with us again, and I'm here to assist you. As a fellow backpacker who understands the struggle of carrying more snacks, camera equipment, and extra socks than necessary, I can relate to your desire to bring your backpack on rides like
TRON Lightcycle / Run and
Guardians of the Galaxy: Cosmic Rewind without any issues.
According to
Walt Disney World Resort Property Rules, you should be good to go carrying your backpack around, including on rides, as long as it's no larger than 24" long x 15" wide x 18" high (61 cm x 38 cm x 46 cm). I personally use a full-size Samsonite backpack that comfortably fits an 18" notebook, and I've never had any problems on any rides.
For some attractions, you'll need to store your backpack in a locker, which is free of charge at the moment, like at TRON Lightcycle / Run. For other attractions like
Mickey & Minnie's Runaway Railway and
Star Wars: Rise of the Resistance, you can keep your backpack close to you and board the rides without any hassle. It's always a good idea to ask a Cast Member before joining the queue about the backpack recommendations for that particular attraction.
If you're considering bringing a full-size backpack to have access to your belongings throughout the day but don't want to carry it at all times, you might find the
locker rental options inside the theme parks quite convenient. This way, you can enjoy your day without the extra weight.
I hope this info helps with your planning, Bryce. If you have any other questions, please feel free to come back and
let us know. It's always a pleasure to help out a friend like you.
Cheers
Nilson