In antistatic bags, in a cardboard box - usually something like an old mobo box, or shipping box.
If I run out of antistatic bags, then I substitue aluminium foil (making sure that there are no batteries on the board first).
There are 2 types of antistatic packaging - metallic and non-metallic. It should be obvious which you have, because the metallic plastic looks shiny - like it's coated with metal. The non-metallic packaging only offers low grade protection against static, and may not protect a very sensitive device (like a CPU or hard drive) enough to allow it to be placed in a plastic box (like a tupperware).