You can get these items by collecting Hidden Packages:

Body Armor: Collect 30 Hidden Packages
Shotgun: Collect 40 Hidden Packages
Grenades: Collect 50 Hidden Packages
Molotov Cocktails: Collect 60 Hidden Packages
Assault Rifle: Collect 70 Hidden Packages
Pistol: Collect 10 Hidden Packages
Uzi: Collect 20 Hidden Packages
Mini Gun: Collect 80 Hidden Packages
Rocket Launcher: Collect 90 Hidden Packages