On UPSC exam day, aspirants should pack essentials such as admit cards, valid ID proofs, pens, pencils, an eraser, and a water bottle. They should also include any authorized study materials or notes that aid last-minute revisions, along with personal items like a watch for time management. A valid photo ID is crucial for verification purposes. Additionally, aspirants should consider comfort items such as a cozy jacket or snacks to sustain energy levels throughout the exam.