A single 'liquid' explosive (nitroglycerin) stabilised with cotton, so not really liquid. And other components including the above-mentioned batteries, some wiring and a modified wrist watch; and a detonator ! The nitroglycerin used could easily be secreted in 1 or more <3oz bottles with innocuous labels, just as in the incident you cite (contact-lens solution).

Youssef did not mix two liquid explosives on board the plane.

The current checkpoint might pick up the metallic components, but a slack x-ray operator could easily miss them. A visual 'baggie' examination would probably not find the nitro.