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.
What kind of fuel? Everyone I know tells me gasoline/petrol will start to go bad in six months and will start damaging my car in two years. Crude oil will last millions? of years but we would need access to a refinery and like you said takes a lot of space anyways.
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.
Speaking of apocalypse bunker, I think the movie 10 clover field lane is genius because I used to think how do people fall for seemingly obvious cult propaganda but if I woke up in a bunker and was told to comply I probably would as well.
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.