Following on to a question by caorach I will give you my take on dealing with a serious wound, for example a deep knife cut involving major blood vessels.
The major issue we have is self treatment and the fact that you may well be stalking alone. These are the sort of wounds where you could bleed to death in minutes. Assuming you have a first aid kit you need a decent pressure dressing (ideally) and that kit must be able to be got at one handed (assuming the other is either injured or applying pressure elsewhere) and opened and the contents accessed one handed. Really vital and easily overlooked.
Apply direct pressure to the wound. Your coat, tissues hat or even hand will do. Maintain the pressure whilst getting to first aid kit. Open dressing and apply to wound and bandage tightly. A proper pressure dressing is very useful as it will have a pad attached to an elasticated bandage and often a bar to allow extra pressure to be applied. The old 'ambulance dressings' of a pad on a gauze bandage are ok but harder to get tight especially if self treating.
Bleeding is continuing. You need to add more material over the existing. Do NOT remove anything from the wound. Anything will do here, hand pressure, elastoplast, even your belt. You need to significantly slow the flow of blood. If it keeps coming through keep adding and getting tighter.
You won't find this in any Red Cross or St John's manual but use a tourniquet if wound on an extremity (arm or leg only). Commercially available ones can be bought (CAT are common) and are easy to use, but you can improvise easily with a drag rope, shoelace etc. Best to tie it then use a bar to tighten. IF YOU USE A TOURNIQUET LEAVE IT TIGHT - your arm or leg remain viable for a couple of hours.
They are a tool in your armoury but don't go with just them and nothing else. Initially they generated a lot of heat, but have supposedly been improved now. There can be issues with retention of the product as keeping a granular material in a wound requires a dressing on top. The impregnated gauze looks promising, but I have no experience. If they are used they form a major contaminant that would have to be flushed from the wound in theatre - you are badly contaminating the wound. There is a theoretical risk that if large vessels are compromised the product may be carried elsewhere in the body and act like a clot. Haemostatic agents are better than death, but no substitute for direct pressure. Wounds in the groin are harder to dress and may make you reach for the haemostatic sooner.
Video of pressure bandage application
CAT Tourniquet vid
Nothing beats training and carrying the correct equipment.