You do not control another Drake or have a Drake in your graveyard.
You have another creature card in hand that is not a Drake and that does not share a creature type with a creature you control or a creature in your graveyard.
If the additional creature has multiple differently colored mana symbols in its mana cost, an additional mana of each but one of those symbols will be required.
Mana Needed
({U} magic symbol) plus enough mana to cast the additional creature available.
Steps
Cast the additional creature by paying its mana cost.
Volo triggers, copying the creature spell.
Resolve both creature spells.
Activate
Food Chain by exiling the creature token, adding at least one mana of any color that can only be spent to cast creature spells.
Cast
Shrieking Drake by paying ({U} magic symbol) .
Volo triggers, copying
Shrieking Drake.
Resolve the copy of the
Shrieking Drake spell.
When the token
Shrieking Drake enters the battlefield, it triggers, returning a nontoken creature from the battlefield to your hand.
Activate
Food Chain by exiling the
Shrieking Drake token, adding ({U} magic symbol) ({U} magic symbol) that can only be spent to cast creature spells.
Resolve the original
Shrieking Drake spell cast in step 5.
When the nontoken
Shrieking Drake enters the battlefield, it triggers, returning itself from the battlefield to your hand.
Repeat.
Results
Infinite colored mana that can only be spent to cast creature spells.