Assuming nitrogen is an ideal gas, we use the relation PV=nRT tp predict what will happen to the system. From the equation, nR/P is constant. So, if the sample is cooled to 72K then volume would decrease. This decrease in volume would affect the density of the substance. It would increase its density. Therefore, the answer would be density.
In order for me to answer your questions I would need to know Whom you are talking of, what they were carrying and why they were doing it so that I could help you understand as to why it would help them to carry these before mentioned things. <span />