I had a secondary job once, inspecting damaged freight, taking photos, and writing up a report for the insurance companies. All I needed for the job was a clipboard, a Polaroid camera, and some forms.
In all the time I did that job, only once did someone ask me for ID before I entered the area where the damaged items were stored. I was amazed at the way a simple clipboard opened up so many doors. Private homes, hotels, loading docks, factory floors, an industrial lab, the local airport, even the police station once.
The one time that I was asked, I told her that truth--that this was a part time job and I didn't have anything to show her. I also told her that she wasn't going to be paid for her damage claim unless I took a photo and wrote up a report. She let me in anyway. For all she knew, I might have been Jack the Ripper, of even a Ninja.
Steve