I used to keep a stock of $2 bills around specifically to pay bus fare - with the bill and a couple quarters in hand, I could step onto the bus, pay, and move back to a seat with barely a pause. This sometimes confused the drivers.
The US has a $1 coin, but stores never give it back in change, using $1 bills instead. Some vending machines do give it back in change.
Indeed, I'm a fan of the USD Kennedy half dollar but haven't seen one in years