When you go to the grocery store or other retail stores and you see clerks stocking items to the shelf ask for their boxes. Most of the time it is store policy to give boxes to any customer that asks. You can also call a store in advance and some will save them for you. Sometimes you can even get star-foam and bubble wrap to recycle. Plastic grocery bags can also be used as bubble wrap. If you put your item in a bag and tie it with some air in the bag then stuff that bag into another and tie and then another and tie it provides great padding for your items. I have even used paper bags to wrap small books or other small items. Wrap it , tape it shut and print the address right on the bag.
While it is ok to save money getting free shipping supplies it is not ok to be sloppy with your packing. Make sure all boxes are sturdy and sufficient packing material to make the box feel solid. If you feel comfortable using your packaged item as a football then you did a good job packing. Most people have seen the awful home videos of delivery men throwing and mishandling packages. Assume your delivery person will be irresponsible. Make your item impossible to break. I have started using duct tape and lots of packing material on my heavier boxes and have had nothing damaged so far with this new technique. While you should fill your box with packing material do not overfill as too much inside pressure can cause the box to burst as well.