They're prepping for the first week, and amassing guns to take from more prepared people after that. To them, Doomsday is their opportunity to go Mad Max style. They're looking forward to being the bad guys in every post-apocalyptic film, the raider group everyone runs and hides to avoid.
It will be our obligation as a collective to seize their excessive wares anyway once the chaos of an apocalypse is over, so I guess they can have fun in their final stand