Currently, my GMail labels are: Financial, To Do, Work, Delete Me, and Really Delete Me.
Everything I receive gets labelled and archived. When I run out of
space, "Really Delete Me" will get purged first. Then "Delete Me" will
be renamed "Really Delete Me" and a new "Delete Me" will be created.
Email that I don't need gets labelled "Delete Me" by default, unless I know it can go in "Really Delete Me."