In Dead Rising 2: Off The Record, Zombrex is the most important item you should know. It is anti-zombie infection drug and you are required to take a doze of when you are infected to keep yourself from turning into zombie.
There are several locations, you will find this drug at. You only need one doze to unlock the corresponding achievement or trophy but I would try to add as many locations as possible where you can find Zombrex.
Dead Rising 2: Off The Record Zombrex Locations
Location. Search inside the Pharmacy at Roy’s Mart.
Location. You can purchase one doze from Pawn Ship in Moe’s Magination. It will cost you $50,000.
Location. Search inside bank vault security box number 673. You will find the key to unlock this box as you follow the reported by the exit to central security room.
I will update this guide with more when I find them. Meanwhile, you can share your explorations in comments below!