During the game, press the [~] (tilde) key to bring up the console, where you enter:
Cheat Codes to “Instinct” Free Download
give weapon_pistol – Beretta
give weapon_ak47 – kalashnikov
give weapon_hk – HK assault rifle
give weapon_m16 – M4A1
give weapon_shotgun – shotgun
give weapon_sniperrifle – rifle
give weapon_crossbow – crossbow
give weapon_minigun – minigun
give ammo_beretta – ammo for beretak
give ammo_ak47 – Ammo for AK47
give ammo_hk – ammo for the HK assault rifle
give ammo_m16 – Ammo for M4A1
give ammo_shotgun – Shotgun ammo
give ammo_sniperrifle – for rifle
give ammo_crossbow – for a crossbow
give_ammo_minigun – for those who love meat