Before watching the movie:
Grill some hamburgers, butter some corn, …load some muskets? warm up your singing voice? A brief look and page turn at your calendar will point out that next week is Independence Day. And what better movie to mark the event with than 1776? Okay, there are better choices, but I’d seen most of the ones that came to mind and/or couldn’t get them on short notice.
I can see the potential for the War for Independence to be a musical epic, but no individual major events really suggest songs to me. The writing and signing of the Declaration will probably have centerpiece song(s), but beyond that, I have no idea.