A medicinal gauze that instantly stops light bleeding, but will require more than one to stop severe hemorrhages. It's a good idea to take a number of bandages for excursions into territories where you will face a lot of opposition.
Shadow of Chernobyl
In Shadow of Chernobyl, it restores a small amount of health and stops the bleeding of wounds. It is also cheap and quite easy to accumulate a large number of bandages. In fact, you might end up stocking quite a few in the end-game parts.
In Clear Sky, it does not restore health anymore and only stops the bleeding of wounds. Bandages are also less likely to be accumulated here in large amounts as bandages have a base cost of 400 RU, though lessens depending on the trader.
Call of Pripyat
In Call of Pripyat it takes time for it to stop bleeding, but it's more effective at doing so.