Serious question: what value would gold have in a post-apocalyptic world? If I'm selling something, why should I take gold in exchange for it, instead of something useful, like ammunition or food or water?
Though now that you point it out, maybe I would rather buy rice and beans so that I could be more useful to people, rather than just maximizing profit. Or better yet, stock up on both kinds of goods.
This expectation may not hold, but whatever the post-apocalyptic world settles on first will likely be there to stay for a while.
What if the people who want your goat don't have what you want to immediately consume but you know for sure Bob down the street (who doesn't particularly like goats) will trade ammo for gold?
Or perhaps your goat ate all your dollars...
Ammunition is better, but for something that can be stored indefinitely without great care, it's hard to beat gold.
Not if you take the time to prepare them. Grains will last basically until pests eat them, and water will last forever if you keep it in a sealed container and sanitize it first. Hell, even meat can keep for years if you salt it enough.