Question: Is money concrete or abstract?

I think money in general is an abstract concept. Societies incorporated money to simplify bartering, where two pounds of wheat was two pounds of wheat and a goat was a goat. Money is a representation of wealth; people no longer need to carry around wheat or goats to trade. They can use the value of the wheat or goats instead.

Was your father protesting because you didn't spend money on groceries at all, that instead you spent it on gas? That would make the argument:

I gave you $50 to spend on groceries.
You spent $50 on gas.
You spent nothing on groceries.
Therefore, you didn't do as I asked.

In that case, whether money is abstract or concrete makes no difference. Your father gave you $50 in exchange for groceries (that he was essentially going to give right back to you), and you had no groceries.