If I rent a movie with iTunes, can I watch them without WiFi on a plane?

When you rent a movie and download it on your device or computer, then you have 30 days to play it. Careful, once you press the play button, you have 48 hours to finish it (or watch it again, if you like). Unlike Netflix it's not a streaming service, so you definitely don't need Wi-Fi. I recommend downloading it on a computer and then transferring it to a device.