Bigger is always better. That being said ,if I were to start over from scratch I would invest heavily in 9mm. Why? how bullets work is they make a hole and let blood etc out. 9mm does that. 9mm weighs less than 40S@W and 45acp so pound for pound there is more shots per pound. The old fashioned run what you brung as previously mentioned is what will be. I think we put too much into shtf rather than just being prepared and stocked up for possible disruptions like in the years before we became mindless mass consumers .