Hey there, hi there, ho there, Sonya! You're as welcome as can be here at
planDisney! Thank you so much for stopping by with your question.
You'll find that the
TRON Lightcycle / Run lockers are much, much bigger than they appear. I can usually fit two medium-sized backpacks, two water bottles, and a merchandise bag in one locker, and there's usually extra space left. That being said, there is no restriction to the amount of lockers you can use if your party's items don't fit inside one. If your plan is to get four lockers from the get-go, I think you shouldn't have an issue!
However, if you do find that one of the backpacks definitely doesn't fit inside the lockers (which is very, very rare), a friendly Cast Member will take it to the exit of the attraction where it will be waiting for you. If you're still unsure and you don't want to leave your backpack with the Cast Members at the exit, you could always
rent a locker by the entrance of Magic Kingdom Park and store it there while you ride TRON.
I hope this helps, Sonya! Go beat the Orange Team for me. Happy planning!
Warm hugs,
Ana Paula