well, they wanted it to be in a place where your medic/buddy could just grab it and use it if you got hit. each soldier was supplied with 2 before the jump, one was usually kept visible and accessable, like on the helmet or tied to the suspenders. it contained a field dressing, morphine, and a tourniquet.
It is the invasion first aid pack. Contains a tourniquet, bandage, and a syrette of morphene, sometimes wound pills(usually to keep you calm) and instructions on what to do. Looking at the majority of pictures of paratrooper, you see this few and far between. Yes...sadly, the majority of pictures shows it on the infamous Easy Company of the 506th.