This page of the Valheim guide will show you how to get a Bloodbag – a useful ingredient used in cooking.
Bloodbag is one of the items that can be obtained while exploring the vast world of Valheim. Bloodbags are used as one of the ingredients for making a Mead base, Blood pudding, and Red banner.
Bloodbags can be obtained by defeating Leeches - enemies that can be found in the Swamps biome. Since these creatures are highly poisonous, it's a good idea to eliminate them with a bow - especially since they can only move in the water.