3. Understand how promotions are actually priced
Supermarket promotions are not random generosity. They follow patterns you can use, once you know what each type is for.
Multibuys — three for two, two for $5 — are designed to increase volume. They are genuinely good value on non-perishables you will definitely use: tinned tomatoes, pasta, toilet roll, washing powder. They are poor value on anything fresh, because the third item spoils and you paid for it. Check the unit price on the offer against the single-item unit price; a surprising number of multibuys are within pennies of the normal rate.
Loyalty pricing, now standard at most major chains, splits the shelf into a member price and a higher public price. The member price is usually the real price, and the higher figure exists to make the discount look larger. Sign up for the card at every store you use regularly, keep it in the phone wallet, and ignore the percentage on the label.
Yellow-sticker and reduced-to-clear markdowns follow a daily rhythm that varies by store but is consistent within a store. Ask a member of staff when their reductions go out — most will tell you plainly. Two passes happen at many shops: a modest cut in the early afternoon, a deep cut in the last hour. Buy only what you will cook or freeze that night, and check that meat and fish feel cold, not cool.
The one promotion to ignore entirely is the end-of-aisle display. That space is paid for by suppliers and is rarely the best price in the store for that category.