At Bristol we do not allow covered drinks into the RZ. I.E. Cups of take away tea and coffee with lids on, open cans of coke etc etc.
Airport security will never be fool proof, at the end of the day we are only a deterrant, but it is significantly harder for a terrorist to succeed with their plans than it used to be!
As for petrol, how did that get on board? Thats dirty cargo, it cannot travel AT ALL.
As for quickly getting through security by not wearing certain shoes or belts that may activate the AMD, you can forget it! Thanks to Smiths detection, there are now AMD's that activate at random! They are a pain in the backside. Not to worry!