At the time of this short, snack stands sold food for a quarter (0.25¢). The subway fare, at least in NYC, was twenty cents in 1968.
Pinky's antics outside the subway car have been done for years by daredevil types across the globe. It's called subway surfing and can be very dangerous, as most extreme thrills are.
This short might be a wink at a popular silly takeoff song at the time. On Top of Spaghetti sang about a wandering meatball; it parodied the traditional folk song on Top of Old Smoky.