What should I do at home on Kartik Poornima if I cannot travel?

Wake up at Brahma Muhurta, take a purifying bath (even at home), light a ghee lamp before Lord Vishnu, chant the Vishnu Sahasranama or at least the Damodara Ashtakam, offer Tulsi leaves, and make a donation to a Brahmin or temple. If possible, keep a night vigil with devotional songs. Simultaneously, have a Pandit perform the Ganga Snan and Deep Daan on your behalf.