This day is really really important, because plastic bag and bottles are one of the main reasons for the existance of the plastic soup and plastic islands in the oceans. Plastic takes a very long time to decompose, and therefore stays in the environment for a much much longer time than human beings ever had hoped and ever expected when invented this great but also risky and hazarduous material. Think about your waste, think about the environment and do something about it especially on this day.
Their page on facebook: https://www.facebook.com/plasticbagfreeday
The event by Zero Waste Europe (Action plan for EU): http://www.zerowasteeurope.eu/2012/06/join-the-3rd-of-july-international-bag-free-day-2/ (really interesting website!)