A saved poster is not an offline movie
My List remembers your selection. It does not store the movie or television episode on your device. If you will be away from a connection, open the viewing options while online and check whether your chosen service supports downloads in its app.
Before you leave
Select the exact production and season, then finish the download on the device you will carry. Open it once to confirm the audio and subtitles. Check the app's remaining-viewing or expiry information, because a completed download can still have a time limit.
Storage and battery are separate limits. Leave room for the full selection and avoid assuming that one downloaded episode means the whole season is ready. Some apps distinguish individual episodes from a season-wide download.
What the Supernova backup contains
The text backup contains title identifiers and your episode checkpoints. It is useful for moving My List between browsers, but it cannot be played as a video. For a connected evening instead, open a movie or series and use Watch now.