The Clingfilm and tape thing is what security do after they bust open your bag.
Printable View
The old biro trick is quick and you wont notice it until you open your bag at home and your stuff is gone.
Believe it or not, some people go to the bother of sewing the zip up. Youl'd want plenty of time and would probably attract the attention of the security forces. Not every airport has shrink wrapping facilities.
Best advice is to keep valuables in your hand luggage.