In these days of looking at the use of recyclable packaging materials, then you could consider using wooden crates instead of cardboard boxes. They can be reused many times over, and are extremely durable.
In addition, if they are built from wood from sustainable forests then they can be classed as green, and possibly even offset against your companies carbon footprint.
They are ideal for shipping heavy goods, or delicate goods that need the ultimate in packaging to safeguard them in transit. They are often used for packaging goods to send abroad, as they can easily be nailed back together if they have to be opened by customs.
They are also ideal for you to use as packaging if you are regularly shipping goods too and from the same locations. It could be you send your customer goods in a wooden packing crate, and he regularly sends items back to you in them, such as an item that needs regular servicing as an example.
Another example is that you may send goods to a supplier for them to carry out work on and that they then have to send them back to you once they have completed the work.
In such an instance a wooden crate for packaging the goods makes far more sense than using a new cardboard box each time the parcel needs to be packaged up.