A Mage is a skill-based dwarf. The best equipment for this dwarf are the Mithril Wizard's Staff, bag of elixirs, and magical elixirs (Elixir of Fire, Elixir of Ice Arrow, Health Elixir, Mana Elixir, etc).
Mages will decide when to use elixirs, it is not possible to control this. They can heal another dwarf with a Health Elixir, transform an enemy into a slug with the Elixir of Transfiguration, or cast magic attacks with Elixir of Fire and Elixir of Ice Arrow.
Unlike arrows used by archers, it is also not possible to disable potions in the "Equip" interface.