If you are caught in an emergency situation where you are stranded and can't get home chances are a backpack filled with life sustaining supplies (food, water, shelter, warmth) will be of much more value than a few guns and a couple thousand rounds of ammo stashed in the spare tire compartment.
I prefer both (although 1000 rounds is more than I carry, it's more like a box for just in case). It's just another item in the auto emergency kit is all. Right up there with the 1st aid kit, the flares, ect. And yes, there's a few water bottles, some granola bars, and an emergency blanket in there too. It's all about emergency preparedness.