Box
You've probably already sent something by post, i.e. a parcel. Boxes are extremely practical. You can open them at the top, insert the items to be sent, pad them a little if necessary so that the goods are not thrown back and forth and they are easy to seal. The parcels are also convenient for transport organisation: they are easier to stack than bags or large padded sacks or envelopes. So everything speaks in favour of the box. But beware: the size of the box is only one thing that is relevant as an indication of the suitability of a consignment. The weight also plays a role, of course. If the box is too thin and the item being shipped is too heavy, the box can be damaged very easily and the goods will fall out and break. Sometimes people are also overestimated, simply because of their appearance. So be careful and don't overtax others when you give them orders. Let them be appropriate to the person.
I wish you an extraordinary day!