Even better--just use wine bottles. I've gone through security with 11 (that's right, eleven) bottles of wine in my carry-on. It's perfectly allowed (there's no FAA or TSA restriction on volume of low-alcohol content bottles carried on board, like wine and beer), and nobody batted an eye.

All the bad guy has to do is replace the wine with the flammable liquid of choice, use a cheap corking machine to recork, and carry aboard. For bonus points, bad guy uses flammable liquid in bottles plus cotton clothes in bag to make molotov cocktails. Bad guy gets super bonus points for using broken bottles as bladed weapon which is much more effective than any puny box cutter , pocket knife, or knitting-needle-of-death.

Such examples are exactly why security screening should be restricted to eliminating obvious threats and weapons, like guns, large knives/swords, actual explosives, explosive detonators, obvious caustic/hazardous chemicals, etc. It will always be possible to construct extremely effective improvised weapons unless the pax, flight crew, aircraft interior, and gate areas are stripped completely naked.

Mankind has been constructing improvised weapons from his environment for hundreds of thousands of years; it's an innate skill that will not go away.