Food spoils too fast. Guns and ammo are not legal to purchase for most. Fuel is a better asset, but takes a lot of space. One good thing about gold is that it's compact.
Depends on what you mean by food. If you have enough time, food can be multiplied. One potato, properly handled, can turn into a field of potatoes. One walnut, properly handled, can turn into a forest.
I think the idea behind an apocalypse bunker is it will remain unsafe to go outside / farm using solar power for a few months to a couple of years but not forever.
I agree. You have to start farming at some point.