They also run special promotions which you can qualify for when you spend more than 50 lira in one go - not free, but very cheap.
For example, I have had in the past a kilo of minced beef for 5 lira; a 5 litre can of sunflower oil for 7 lira; a pack of 12 cans of Coke for 5 lira. Also, you are entitled to this for every 50 lira you spend, so if you spend 200 lira you can have four of whatever it is they are offering.