Give every item on the shared list three things: an amount, a state — needed, being bought, or bought — and the time the state last changed. The handover is the point, not the format. What it protects against is the largest block in the UK data: food not used in time, which is 953,000 tonnes that looked or smelled off plus 758,000 tonnes past the date on the label, 39% of the 4.4 million tonnes of edible food UK households binned in 2022 and £6.86 billion of the £17.5 billion total, in WRAP's UK food waste key facts. The condition that changes the method is whether both people shop from home: two shoppers leaving from different places need a timestamp, and one shopper leaving from the kitchen does not.

Three states and a time stamp

Needed means nobody has it yet. Being bought means one named person is in a shop with it in mind. Bought means it is in the house. Write the name and the clock time beside the change: "Sam, Tuesday 16:10". Without the time, two people can both be honestly reading the list and reading different lists.

Choose the place before the format. A sheet on the fridge works when shopping starts from home; a shared phone note works when someone stops at a shop on the way back. If one person will not use the chosen tool, the agreed fallback is a message before entering the shop. Age does not decide who uses which.

Avoid two authoritative copies. If someone photographs the kitchen sheet, that photograph is stamped with the time it was taken and stops being the list. Otherwise "the list said so" is true for both people while the list itself is out of date.

Give each person one standing job: one resets the list after the shop, the other writes the amounts when the meals are planned. Rotate the reset, or do it together while unpacking, so the invisible tidying is not the price of everyone else's convenience.

Write an amount, not a noun

"Milk" invites two reasonable and different purchases. "Milk, 2 litres, none at home" invites one. The amount describes the remaining need, not the pack; deciding which pack covers it is a separate calculation set out in when pack sizes do not fit your household.

The items worth this care are the recurring ones. In the 2022 UK data the ten most wasted items in homes start with fresh potatoes, meals, bread and milk, and fresh vegetables and salad alone are 28% of the edible food thrown away at home by weight (key facts). Those are also the items two shoppers duplicate.

If an item is unavailable, move it back from being bought to needed and say so. If a substitute is bought, write what arrived. Leaving someone expecting the original is the same failure as not writing the item at all.

When dinner changes, one message updates the list

A cancelled meal does not delete its ingredients. The person who planned it names the items affected; the person shopping answers whether they are already in the trolley. "Wednesday is cancelled — have you bought the salad yet?" asks for a state change without assuming where anyone is standing.

If no answer comes back during work or travel, the default is to hold non-essential additions until it does. That default is written into the agreement once, so nobody has to invent it in a shop.

An example handover, and what a duplicate costs

An example list, with every figure worked out. Two people each buy an 800 gram loaf on the same Tuesday and one goes uneaten. At the UK 2022 value of edible household food waste — £260 for 65 kilograms per person, so £260 ÷ 65 kg = £4.00 a kilogram — that loaf is 0.8 kg × £4.00 = £3.20. Once a month it is £3.20 × 12 = £38.40 a year; once a week it is £3.20 × 52 = £166 a year.

Read the same figure against the EU picture before deciding how much effort it deserves: EU households produced 53% of the 58.2 million tonnes of food waste generated in 2023, 69 kilograms per inhabitant of around 130 kilograms across the whole supply chain, per Eurostat's release of 16 October 2025.

After two or three trips, check one specific thing: was anything bought twice, and which update was missing when it happened. Keep the three states if the answer names a missing update; simplify to a phone call if maintaining them costs more than the £38 a year. A week of entries, as in a week of less food waste, together, tells you which of the two you have.

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