The Collectible Item in Angry Birds Star Wars 2 Rebels level BE-5 is attached to some stone floating towards the top right hand side of the level. This one requires some luck to obtain, as you have to use to debris from the explosion to hit it.
Go back to the Complete Star Wars II Bonus Boxes Guide. If you have a different strategy feel free to leave a comment below.
Use the first bird or two to clear everything in the center. Then attach a detonator to the bottom of the rock that holds the bonus box, as far to the right as you can. The force of the blast is enough to get the box.
Did that. It worked first time.