Local Travel
Buy a local metro card! Some American cities have a useful and efficient public transit system, but many do not. Many cities across the globe pride themselves on their metro systems. Some cities charge extra for a "tourist" metro card, but it is possible to get the standard metro card for cheaper if you only know to ask for it. Paris is a culprit of this (pictured below).
Don't be afraid to use the metro to get to and from the airport either! Rideshare services are available globally as are taxis and can sometimes be more economical, depending on the number of metro tickets you're buying, but often, this is not the case. Ride the train!