How can I unstick a backpack zipper?

To unstick a backpack zipper, try rubbing a bar of soap or a pencil along the teeth of the zipper to lubricate it. Gently pull the zipper back and forth to see if it loosens. If that doesn't work, try using a lubricant like WD-40 or silicone spray. Be careful not to force the zipper as it may damage it further.