If, as Mike S says, your Stack is an interface, that makes it easier for you, because "Stack<E>" will cover all types you ever need.
Write down on paper what your definition of equals is: what features of a stack will lead you to believe it is equal or unequal to another stack? And remember your method will have to deal with
null values; in all cases you are looking at
You can write yourself an Objects class similar to
that planned for Java7, which probably uses the same formula for its equals(Object, Object) method.