At some airports they search where you can watch. They won't let you "be" there regardless, and you will not be permitted to touch your items once they start screening, eg to repack.
You can offer "help" which they will ignore and tell you to go away after, but usually if they know you're there and watching, they will be that little bit better about handling your stuff. Unfortunately, the airports where you can watch are becoming fewer and fewer as they finally make their desired changes to move their inspection behind the scenes.