Blood bags are an item added in The Crafting Dead which help the player by giving the player blood.
Blood bags are used by right clicking when the blood levels are below 100%. Blood bags will restore the player 33% of their blood, but after a blood bag is used it becomes useless to the player. Blood bags are gained from medical loot found on the ground in naturally generated buildings. Be careful because if a wound isn't bandaged, blood bags will only delay the inevitable.
blood bags can also be used when empty to steal other players blood and fill the blood bag