During my prior visit to Manhattan I had seen a sign, that wasn't there on the second visit, that sign mentioned something about the storage box being for storage of local civil emergency equipment. The backhoe sign might be where that sign used to be.
The redundant HVAC units made me think of ammunition, tear gas, etc., in case mostly peaceful protests break out in Manhattan, Nevada. But that signage was not to be seen later.
Could of been used for emergency medical, water and food supplies.
Most residents probably have their own cache of supplies and tools.