Every time I get a parcel I keep the carton. Every time I get a letter I keep the envelope.
I think that’s one of the easiest ways to do something for nature: Just reuse old shipping supplies. They are quite expensive to buy new, so it’s a relief for your wallet as well. In my family there is even a special carton that we use for years now – it’s a real stable and pretty one with a nice flower pattern and a good size for most things.