What did Holden leave on the subway at the beginning of the novel?

At the beginning of the novel, Holden leaves the fencing team's foils and other equipment on the subway. Holden is the fencing team's manager at Pencey Prep, and he carries the team's gear during a trip to New York for a meet against the McBurney School. While distracted by thoughts about his life and school, he forgets the equipment on the train.

Because the team has no foils or related gear, the fencing meet cannot take place. The team returns to Pencey early, and Holden faces the anger of his teammates. The incident establishes his carelessness and isolation before the main events of the story begin. It also explains why Holden is back at school while the other students are attending Pencey's football game.

The answer is sometimes misremembered as Holden's suitcase, record, or hunting hat. Those objects are connected to other parts of his journey: he carries luggage to New York, buys a record for Phoebe, and wears the red hunting hat as a distinctive personal symbol. The forgotten items are specifically fencing equipment, with the foils named first in Holden's narration.