Until recently, the computerised tills at Sainsbury's would honour 'n items for £x' special offers even if the items were otherwise reduced. It'd do this by subtracting the difference between the full price and the offer price from the total bill.
On one happy day this meant that they were paying people to take away strawberries: the price they'd been reduced to was less than the amount being subtracted! The result was less wasted food and we had half a freezer of strawberry purée.
But alas, no more. Poo. All this will mean is that people will tend to leave the 'soon out of date' food on the shelves and they'll throw it away.