A medical item for performing life saving first aid in extreme cases of blown or cut off limbs.
In military situations or in a saw mill for instance.
Easily cut open the waterfilled bag, pull it over the remaining limp and tighten the buckles. The water pressure caused by the tightening of the buckles keeps blood from pumping, and it keeps the wound safe and clean.
The different displays of colors are meant to match different environments. At the sawmill (or any other relevant workshop) the bag screams for attention for it to be easily found, and the simple instructions are found on the front of the bag. The military versions are slightly less noticeable, so the wounded won't become an even easier target. Soldiers are trained to know how to use all of the first aid equipment in the medics bag, making instructions unnecessary.
(Sorry for the extremely large pictures)