It is not uncommon to see this weird upgrade to the AK rifles or other Soviet made weapons. Pictures can be found from Soviet-Afghan era and in every other post-Soviet conflict. So what exactly is going on?
Tourniquet on the AK stock
So, the pink band you can see on the AK stock is the Soviet hemostatic tourniquet. It is the direct successor of the German first-aid invention first tested in the Franco-Prussian war and used in the Soviet Army ever since. In Soviet union it was called Esmarch tourniquet and was widely used both in civilian and military medicine.
By the book, the tourniquets were to be issued to the soldiers before the operation and were intended to be stored in one of the outer pockets of the M69 tunic, together with the bandage. And, of course, it was never issued for training exercises - the first aid culture was poor back then and only designated medics knew how to do it.
After the invasion to Afghanistan, Soviet troops found themselves in a very new and dangerous conditions. Many were issued these tourniquets for the first time, and given what sort of uniforms were used in Afghanistan, like KZS or KLMK - there were no pockets for the first aid kit. Soldiers had to improvise.
And this is how the tourniquet started to appear on the stock. When used with a folding stock AK, the bandage was placed inside the stock as an additional bonus. Apart from AK, tourniquet was sometimes reeled to other weapons - SVD, PKM and even RPG.
Why it is a bad idea to use it like that
This soviet rubber tourniquet was not great - it was hard to apply it to the wounded limb, it did not maintain the required pressure well and it could easily rip when overstretched. However, this was still better than nothing - damaged limbs are a regular companions of the war and something had to be done with it.
Now, if you use the Esmarch tourniquet as intended, it can actually be quite helpful, if the conditions are right. But for it to maintain its properties it has to be sealed in a plastic bad and not be exposed to the sun and hot temperatures. Of course, the weather conditions in Afghanistan were rarely beneficial for the rubber tourniquets. By the book and common sense, all of them had to be stored either in a medical bag or in a pocket of a soldier.
While reeling tourniquet onto the stock of the AK rifle seemed like a good idea - the tourniquet will always be close to you, in practice it was a disaster.
When on the stock and exposed to the surroundings, the rubber tourniquet looses its properties almost immediately. After a short while, a week in Afghanistan weather, it will become hard and brittle. So if a soldier were to take it off the stock, most likely the tourniquet would just fall apart in his hands, making it useless for its initial purpose.
The rule is simple - the tourniquet should be stored inside something and not be exposed to air.
Positive aspects of tourniquet on the metal stock
But there were some advantages to using rubber band on a metal stock - as a pad. In Afghanistan, summers can get steam hot and winters can get freezing cold. Metal stock of an AKS-74 will be of the corresponding temperature. So, in order to not hurt your face and actually have the ability to shoot your rifle properly, having a tourniquet was definite a very helpful and practical attachment.
The tradition of reeling the tourniquet to the AK stock became so popular that it is done until that day, even though modern stock do not really need it and modern soldiers usually use CATs. But overall it is fading into the history, just like taping together two magazines on the AK.