Sounds like the beginning of several zombie movies from the 80s. Only a few minutes after driving past, a canister would roll off the truck bed. Kids would later find it.
There was a movie in the 80s about two guys who grew up in a fallout shelter with nothing to watch but Humphrey Bogart movies, emerged years later as noir style detectives, and had to fend off mutants from launching the last nuclear missile on earth.