EquipItemByLink

From WoWWiki

Equips the first matching item found in the player's bags (including the bank and bank bags).
Checks the bank first, then carry-ons, then bank bags.

local function EquipItemByLink(link)
	for bag=BANK_CONTAINER, NUM_BAG_SLOTS+NUM_BANKBAGSLOTS do
		for slot=1,GetContainerNumSlots(bag) do
			local item = GetContainerItemLink(bag, slot)
			if item and item == link then
				if CursorHasItem() or CursorHasMoney() or CursorHasSpell() then ClearCursor() end
				PickupContainerItem(bag, slot)
				AutoEquipCursorItem()
				return true
			end
		end
	end
end