A few more:
Panic in the Year Zero with Ray Milland. Family flees nuclear war.
No Blade of Grass, based on a novel by John Wyndham, who also wrote Triffids. British, all grasses (think wheat, oats, etc) die. Better movie than Triffids.
Damnation Alley; stooopid movie based on an outstanding novella by Roger Zelazny.
And 28 Weeks Later was much better than Days.