Overtime mode

Successfully complete 72 hours in the mall and return to the heliport by 12:00 a.m. on the 22nd to unlock Overtime mode.

Unlimited mode

Successfully complete the game with the "true" ending to unlock Unlimited mode.

Katana

Go up to the second floor, then go to Columbian Roastmasters. Go to the where the cash machine is located, then jump out onto the roof/ledge below. Land on the orange overhang, then look for the katana.

Submachine gun

Jump from the stairs closest to you when you start to the blue ledge above Kid's Choice Clothing. Keep following the walkway past the stuffed bear all the way to the end to find the submachine gun.

Uzi

In the Food Court, go to the sign with the Italian chef. Climb to its left side, then to the top to find an Uzi.

Servbot Head re-alignment bonus

In the toy shop, hit the giant servbot until the swirly eyes are lined up with the sad face for 10,000 pp.

Bonus items

Successfully complete one of the following tasks to unlock the corresponding item inside a shopping bag behind the air duct in the Security Room:

Ammo Belt: Do not miss with a machine gun.
Arthur's Boxers: Survive for at least 7 days.
Hockey Mask: Photograph all PP Stickers.
Laser Sword: Survive for at least 5 days.
Mall Employee Uniform: Answer all calls from Otis.
Mega Man Boots: Get the true ending without being knocked out.
Mega Man Tights: Defeat at least 10 psychopaths.
Prisoner Garb: Steal the convicts' vehicle.
Pro Wrestling Boots: Break at least 100 items.
Pro Wrestling Briefs: Defeat at least 1,000 zombies barehanded.
Real Mega Buster: Defeat at least 53,594 zombies.
Special Forces Boots: Defeat a least 15 psychopaths.
Special Forces Uniform: Repel a helicopter.
White Hat: Photograph at least 50 survivors.
Unknown: Get at least 50 survivors out of the mall.