I had to cheat for the first one:
The gems are
Amethyst
Emerald (Emerald city - Wizard of OZ)
Ruby
Pearl (From inside oyster shell)
Diamond
Tiger's eye
Cubic Zirconium (Fake diamond)
Black Opal
Taking the first letter of Amethyst, second of Emerald etcetera gives
Ambrosia - The food of the gods.
Well, duh. They could've just asked what the favorite food for the Greek gods was, and I would've answered it with ease.