This would be the most inconspicuous way to get rich with time travel.

But by buying too much you could throw off the future, so it might be guess and check.

But how? You don’t have access to your current bank account, any cash you bring would likely get marked as fake because of the redesigns that happen.

It is fun to think about “if I go back in time I will buy as much X as possible.” But you don’t have any currency from that era.