Exactly what I was going to mention. I'm surprised the Mad Max Trilogy wasn't mentioned earlier. Any post-apocalyptic or zombie film I consider to be a SHTF movie. Doomsday, Mad Max Trilogy, Resident Evil Trilogy(Apocalypse especially), 28 Days Later, 28 Weeks Later, I Am Legend, Terminator Series, etc.OK- set a few years after SHTF, but a lot of fun: Mad Max
Army of Darkness and Evil Dead....WTF!?!
For us cold-war babies, this is a memorable one:
The Day After
The Day After (1983) (TV)
YouTube - The Day After (Attack Segment)