There are many elements to surviving in potentially deadly or hazardous situations. This is your final layer for a person without using a dog, horse or your vehicle to carry more substantial equipment. The rucksack will vary in size according to your needs at the time, example day trip, hunting, or hiking in to camp. More detailed medical gear can now be carried, rope & assorted mountain climbing equipment. Extra clothing, fishing poles, rifles, bows, extra food and water just to name a few items.