Get and keep a copy of a movie on a hard drive or Blu-ray somewhere. If you “purchase” movies through sites like Amazon Prime or Apple TV/iTunes (RIP) you’re merely licensing it and they can take away your access at any time for whatever reason they want.
I don’t advocate pirating movie content you don’t already own, but if you own a copy of a movie or show, go ahead and download a digital copy to back it up somewhere so they can’t take it away from you.