@cardibach , You use the loyalty points against your shop. If my points add up to £5, and my basket adds up to £30, I pay £25. It doesn't matter much what I have in my basket.
The supermarkets I shop in don't offer bonus points on one product over another. I will sometimes buy things that are priced down if I use a loyalty card, but they tend to be things I buy normally.
I weigh pre-packaged items, and work out cost per kg when I put items in my basket. I also buy loose veg when I can.
The fresh food being expensive/goes off too quickly argument is another tedious one. Carrots, for example, are about 10p each.
Carrots tend to be a loss-leader, as is milk. The supermarkets can do this because they have the power over farmers. They don't have this power over the large international companies that make baby formula.