Various ideas (some may only be appropriate in some seasons) mostly centered around the NYC area — but some can be done anywhere:
Go upstate to Harriman State Park or Bear Mt. State Park (or some other nice park area near you) and hike and take in the beautiful fall foliage.
Picnic — with lunch and board games.
Take a Circle Line cruise around Manhattan
Observation deck of the Empire State Building
Catch an IMAX movie (Liberty Science Center usually has a good “non-entertainment” IMAX movie playing all the time).
Go to a drive-in movie (there’s one up in Warwick, NY).
Dinner followed by a star-lit stroll.
Classical music concert performance.
Bowling
Pottery painting
Share a large ice cream sundae
Take a ride on the carousel in Central Park
Walk on the boardwalk
Purposely get caught in a rainstorm.
Eat a picnic on the beach, listening to the pounding surf
The Wolf