You are a lot less likely to take a Roku or Xbox to a friends' house to watch Game of Thrones, but you always have your iPhone But if you have access to HBOGO

You are a lot less likely to take a Roku or Xbox to a friends' house to watch Game of Thrones, but you always have your iPhone But if you have access to HBOGO as a HBO subscriber in the first place, you could just log in to the website on your friend's laptop (or Roku, or Xbox) and watch the same content that way.