The farmer and his entire family will always need food, for the rest of his life at steady 4 to 12 hour intervals, and if he was too hungry to drive his daughter might just as well have died.
Just because I currently value a bitcoin as worth more than 5 breads does not mean bitcoin is more valuable as a commodity. Bitcoin has no value for most people in the world.
I will always need bread, even if my internet access is cut off or there is a massive shortage of electricity, I'll manage without bitcoin.
However, you or I can't manage without bread or other food. We can manage without bitcoins. Hence bitcoin has subjective value (up to market to decide) but food is always worth *something*.
If fuel runs out globally, cars become worthless. If there is an attack on electricity networks, all gadgets become useless.
But food can't become useless as long as someone is alive.
Do you realize you are justifying that food has subjective value? You are saying that food is valuable to humans because we need it. That is the exact definition of subjective value.