What are some fun, cheap activities to do with my girlfriend in NYC?

Going to New York City tomorrow to see a show with my girlfriend at 7:30 in the evening. She bought the tickets as a graduation present so I want to plan some nice things to do with her before the production to show my appreciation! We’re on a pretty tight budget so the activities will have to be kinda cheap, but we’re also both college students so anything with student discounts will definitely be considered