To minimise the carbon footprint of your product
or packaging it should be carefully designed:

• to optimise materials required and
  energy consumed.
• from compatible materials or ones that
  can be easily disassembled and reused. 
• to be safe and healthy to use for
  individuals and remain beneficial
  throughout its life cycle.
• to meet the performance and cost for
  its specific market sector.
• to be sourced, manufactured and transported then recycled using
  renewable energy.
• for manufacture from the cleanest production technologies and processes.
• to be produced from materials
  which are not harmful after end of life. 

These are principles and guidelines to consider, they are ot always possible but certainly an accomplishment to aspire to.