The backstory is the part that isn't included in the story. But for the writer, it adds depth and additional ideas.
Sometimes a single item has more meaning than imagined. Symbols of Christmas can remind you of the true spirit of the season.
Ideas don't drop out of the sky fully developed. A process of ten hundred beginnings is what develops ideas. Take the snippet you have and run with it.
A writing skill not many think of, is the ability to be precise. In all writing and communicating, the ability to be concise is valuable.
Writing a movie sounds fun, but it takes a different skill set and understanding the screenplay format. Take a look at a new way of writing.