Believe it or not, Maxim dedicated a whole app note to describing the benefits of using disposable metal boxes as EMI shielded enclosures for your projects. Small steel tins some candy manufacturers use provide both electrical and magnetic shielding:
One way to break this wasteful cycle is use the small steel tins in which candies are sold. These boxes, usually about 4″ wide, 2.5″ deep and 0.5″ tall, can easily contain many of the test fixtures. The lids are hinged, allowing easy access to the internal circuits while protecting the same circuits during storage. The steel construction provides both electrical and magnetic shielding.