If the streets are deserted, before you start to panic about the Zombie Apocalypse or setting extra places for the four horsemen, check the calendar. Is it Sunday?
If it is, you're fine. The world is not coming to an end.
Everyone is at Superstore. And though their manners may make them easy to mistake for Zombies (from any movie, some are the slow moaning ones that are fairly ineffectual and some are the crazy running screaming hardcore ones), don't worry your silly head. They're just assholes.
On an unrelated note, there is nothing I need badly enough to ever make me try "just running in to grab a few things" on a Sundday again. (If I run out of toilet paper, I'll hold it until Monday.)