To my knowledge, citric acid does not expire so long as it's stored and remains in powder form.
As for Miracle-Mineral-Supplement , if the mixture is prepared in liquid form, then I've read that it will expire in time. Though I've had bottles myself for over three years that appear to be okay.
That said, on way to store Miracle-Mineral-Supplement long term, is to store place in an airtight container and in a cool dry place. Whereas some people say, you should freeze it. Though I can't confirm whether this is necessary or not, as chemical suppliers appear to store it in their own warehouses for very long periods of time(several years) also.