For my youngest, a stick is all he needs. Even at 12, he still loves sticks. They become guns, swords, what ever he wants them to be.
I had to stop him from bringing his collection inside, though. Now, he sticks them into my shrubbery t hide the best ones.
My youngest loves rocks. He has a hard time passing a rock and not picking it up to throw it. There would be times I’d do the laundry and his pockets would be full of rocks.