Not allowed: nail-clippers.
Allowed: to go into the shop after security and buy a large glass bottle of flammable liquid (e.g. vodka) that you could take on the plane and break into a formidable weapon and a fire bomb.
Let's be honest – a lot of the security measures at airports are there either as a PR exercise to make people simply feel safer, or because the security managers wanted to increase their staff numbers, and therefore their own importance.
If someone has a modicum of intelligence and is prepared to die, then there is nothing you can do to stop them killing at least some people.
Why are airplanes targeted anyway? It would be a lot easier to get a van with a bomb in it onto a ferry, or just parked in Wall St. Many people would die, there would be just as much publicity, and you could keep your own life. If public fear and disruption is the objective then I just don't think taking down an airplane is good value for them; these terrorists have no imagination. No logic behind their actions either - if you asked one of the terrorists how what they do is going to advance their cause, then I doubt they would demonstrate a well thought-through logical connection between the act and their aims.
Headline news in the UK today is a bomb last night in Northern Ireland; some Republicans killed a Catholic policeman. While I'm sure they viewed him as some kind of traitor, I doubt they would say it was a simple act of punishment - they would claim it advances their cause somehow... but I highly doubt whoever planted it would have a coherent explanation of how it achieves this.