I still reuse the packing material I get with my purchases. If you get a nice big sheet of bubble wrap and a bucket of those foam packing beans I see no reason to throw them away. I don't think boxes are a serious issue either. I never buy them, I store the boxes that come my way if they are in good condition or pick them up at random places. Everything is free.
As for the time consuming thing, if I sell something it's already packed when I list them on the various platforms. Tested with a lot of good pictures and screenshots taken. When someone buys them I just take a detour to the post office on my way to or from work.