maybe a hard hat for working in demolished urban areas?
A white hat with the red cross would help identify him as a medical professional.

Each persons PSK and FAK needs are different but for this trip I would ensure that they included:
-leather glove work gloves for moving debris
-a water filter and purification tabs, clean water is going to important if the municipal supply is compromised.
-some kind of radio to communicate with local authorities and disaster relief operations.
-a travel/secure wallet, there will undoubtedly be trouble with marauders and opportunists trying to take from a well stocked and relatively wealthy American.
-tough boots....not sure which i.e. steel toe, hiking, etc...would be more appropriate but something suited to the climate and working conditions.