As far as the US would be concerned, there would probably be a blitz of violations against all the Amendments made by government branches in order to assess power AFTER the one-day battle royale. We'd have a bunch of looting, kidnapping, and raping, with some pockets of killing on the side.
Discriminated groups, such as Islamic peoples and the Westboro Baptist Church, will probably be stormed and torched.
Churches, temples, and other places of worship will be filled to the brim with the faithful looking for shelter. Whether they will stand as a valid fort of protection is another question entirely.
Gun shops are big targets, but simply stealing a gun for one day isn't going to do anything except prep people for next year or for some mass-killing off-season.
Don't go to Wal-Mart, Costco, Sam's Club, or any of those other massive retail places. You'll be crushed in the stampede.
If you bring a gun to Gamestop, you'll win half the fight. The other half actually getting to the back of the store without getting shot by other looters.
Restaurants probably won't be open. It's gonna get messy.
Also...prisons...um...
...all the prisoners die by the end of the day, if not raped and horribly tortured.