If you're staying in New York on a temporary basis and need to use cannabis while you're there, you can sign up as a temporary patient. You will have to see a New York medical marijuana doctor in order to be approved, and the process takes a few days, so you should plan ahead. You will be required to show temporary proof of residency such as a rental agreement or utility bill (not a cell phone bill), and the certification will only be valid for the length of your stay.