More than any other category, the packing question here is really a delivery question, and it is answered before the sale rather than after.
Ask the courier first
Many couriers will not carry perishables, chilled or frozen goods at all. Some restrict liquids. Transit times vary, and a parcel can sit over a weekend.
Find out what yours does before you quote a delivery price, because the difference comes off your own balance. If the answer is no, say collection-only in the listing. Setting up pickup.
Then pack for heat
Assume the parcel will spend hours somewhere warm, because it will.
- Shelf-stable only, unless you have a cold chain you can actually rely on
- Insulation for anything that softens, and say in the listing that it is heat-sensitive
- Nothing that must stay cold goes by ordinary courier
Against leaking and crushing
- Caps and lids taped so they cannot turn
- Each item in its own sealed bag
- A second sealed bag around the lot
- Absorbent paper inside
- Rigid box, voids filled, heavy items at the bottom
- Every seam taped
Glass bottles get bubble and a box, never a soft mailer.
Against pests and damp
Sealed bags are not only for leaks. A box of dry goods that has been open to the air in a humid month arrives with a problem, and a sealed inner bag prevents both.
Label the outside honestly
If a courier requires perishables to be declared, declare them. A parcel that is refused mid-journey is a parcel that spoils.
Questions people ask
Can I use ice packs?
Only with a service that will actually move the parcel fast enough, and say so in the listing. For most sellers the honest answer is shelf-stable or collection.
Should I include a best-before note in the parcel?
Yes — a line with the date and how to store it, as well as what is on the pack.
What if it spoils in transit?
Your photographs, the date and the service you used decide it. How returns work.