Apparently none of those according to zerohedge:
http://www.zerohedge.com/news/2017-04-29/last-remaining-cheap-assetThe article does not mention bitcoin since it is an highly speculative asset but it says that every other asset out there already overpriced because of the FED's money printing policy. Every other asset but "grain".
It doesn't make sense to me to fill my home with grain bags though it might become handy in wwIII.
If all assets are overpriced, Bitcoin is too. Because of quantitative easing, money has flown into almost all assets.
The only reason why grain prices haven't taken off is that governments will not allow a basic need like food to become very expensive.
You forget one circumstance that it is the government that is cashing in on the sale of food products, including grain, and the people of the country that is the producer.