If one really wants to make international flying perfectly safe (at least safe from terrorists masquerading as passengers), it is in fact very simple and quite cheap:
* No carry-on or check-in luggage at all (all kinds of chemical, bacteriological or radioactive materials could be hidden there, for example it can be trivial to make a laptop burn up in flames mid-flight and make in in non-detectable way).
* No personal items of clothes (clothes can be soaked in certain chemicals to make them explosive).
* Secure passengers during the flight ( so that they can not actually do any terrorist activity).
So, the optimal way of securing air transportation would be to have people come in without any luggage at all, remove all items and clothing at check-in, dress in uniform one-time paper clothing where one can not hide anything, sedate them, feed them trough introspective inspection to detect in-body foreign objects and check the chemistry of skin and hair, pack them into the airplane on secured padded shelves, fly them to the destination, reverse the sedative and give them a standard set of clothes and essential personal items.
In addition to perfect security, this plan will also reduce the overall cost of air travel by allowing to pack more people into an airplane of the same size - the padded shelves can go from the bottom of the airplane to the very top with minimal spacing (all passengers are sedated - they will not walk around), no separate cargo hold will be needed (no luggage) and no in-flight entertainment or food will be required.
If the current security craze continues, we might reach this perfection by 2020. Congratulations!