The speculation that I have seen concerning the hidden idol is that it is in the water bucket back on exile island.
That was the first thing I thought of but somehow it seems too obvious. I think its more likely that they have to use the pot to carry the water to the skull, walk up the steps in the back and pour in in something like a bamboo pipe that will release it after all the water is hauled. Or like I said in my post it may be in the handle of the machete. It has to be very small as these people are being dropped off with nothing and have to return to camp, they have to be able to hide it on their bodies until they get back to camp.