Products you pay for once and take twice.
Every 1+1 offer in one place: buy two of the same product and you pay for one, so the price of a single item halves. The card shows the ordinary shelf price of one, with what it comes to under the offer underneath. The offers are the shops' own: they run for a limited time, sometimes only with a loyalty card or up to a stated quantity, so check the conditions at the till before you pay. The list is refreshed with every catalogue sync, and an offer that has ended drops out of it.