"would improve their chances of surviving a disaster" A 1% improvement is still an improvement. If I think I can survive with X then I'm sure that having X+Y w

"would improve their chances of surviving a disaster" A 1% improvement is still an improvement. If I think I can survive with X then I'm sure that having X+Y will lead to an improvement in my ability to survive. (Assuming I don't have to lug the extra Y around with me.)