Do not buy a packaging kit. Buy for the first ten parcels, find out what you actually send, then buy properly.
The starting list
Boxes in one or two sizes, matched to what you sell. One size that fits most of your range is worth more than six that cover everything, because choosing slows you down.
Bubble wrap or paper. Paper is cheaper, recyclable and fine for most things; bubble wrap is better for glass and glaze.
Good tape and a dispenser. The one place not to economise — cheap tape fails in transit and a box that opens is a lost item.
A scale. Kitchen scales do. You need the real weight, because the courier will find it anyway and bill you the difference. What is chargeable weight?
A tape measure. Couriers charge for size as well as weight.
That is the whole list to start.
What to add once you know your range
Poly mailers for soft goods — far lighter and cheaper than boxes, and the saving is real because the box is often a third of a small parcel's weight.
Corner protectors for frames and flat things.
Resealable bags for anything that must stay dry.
Tissue and a sticker, if presentation is part of what you sell.
The one thing worth spending on
A box that fits. Not the cheapest box, not the one you have.
An oversized box costs twice: more filler, and a higher chargeable weight because the courier bills the space. Dropping one dimension by ten centimetres can be a meaningful saving on every parcel you ever send. Why does a big light box cost so much to send?
Where to get it
Local packaging suppliers are usually much cheaper than online retail for anything in quantity, and many will sell you fifty rather than five hundred to start.
Reusing boxes is fine and sensible. Cover the old labels completely, and do not send something fragile in a box that has already been through a network once.
What buyers notice
Arriving intact, which is 90% of it.
Not needing a knife and a struggle. Over-taping is a real complaint.
Something small and human. A note costs nothing and appears in reviews more than any material does. How to pack an order
What they do not notice is expensive branded packaging on a cheap item — that reads as the cost being somewhere they are paying for.
More: how to pack an order, fragile item delivery, do I need a label printer.