I got diabetes and need to take medicine everytime I eat something (even if I don't I need to take a small dose to keep me going), so I'd have to scavange every apothecary for it. Plus, it has to be kept in low temperature to keep it working and I figure it'd be hard to find a working fridge in a shithole far enough to be safe from radiation. Furthermore, these medicine will run out eventually and I doubt anyone will produce it if all hell break loose. Of course I could be lucky and live for couple of months or even years, but I'm fucked in a situation like that anyway.
Or you can make your own...I mean, prepare yourself if you know the war is coming. If they made it in the '30s and '50s sure as hell you can make it in the 21st century. All you need are pigs and cows.
The absence of doctors and medicine would be a great threat. If today you get a nasty cut or a cold, you take a pill or go to the doctor. Imagine if there's no pill and no doctor. That rash could get really ugly...