I have given this some thought and discounting the Zombie scenario this situation would likely happen on the way to work or back or during work, unless you are unemployed or work from home. It is highly unlikely that you have time or opportunity to pick what you want or the quantity you want in regards to ammo and guns. So going with what I always have with me on me or in the car, I would have my S&W SW99 in .45 acp 2 extra mags and a box of 50 rounds in the car a backpack with a couple of days worth of supplies and a week worth of meds. I also carry a change of outdoor cloth and boots in the trunk as I don't want to encounter the TEOTWAWKI in shirt and tie. LOL I have been using and carrying my SW99 for some time and I'm very confident and proficient with this gun even though it is on the larger side of carry guns but I'm a pretty good size guy so I can hide it well. So this is most likely what I have to use in the TEOTWAWKI situation which is probably as much or more then most people will have in this situation. Now if I can make it home everything will change but then I also would not only pack one gun.