You'd be surprised what gets left behind when a place closes. Obviously things like painkillers and copper pipe are going to be stolen very quickly, but it's reasonable to find lots of other things tucked into boxes or cabinets and eventually spilled by environment, animals, or looters. Things like medical supplies that were considered contaminated or written off and so left behind.
Paper should be everywhere. Unused letterheads, medical records, invoices, tons of documents that are too heavy or too numerous to dispose of properly (or people were too lazy) and considered generally valueless are going to be left to rot.