As used in this part, the term "contract" means a contract or subcontract entered into by a county with any person, with the state or federal government or an agency of either, with another county or counties, with a municipality or municipalities, or with any combination of the foregoing entities for the construction, reconstruction, or maintenance of all or part of a public road, including but not limited to a contract for the purchase of materials, for the hiring of labor, for professional services, or for other things or services incident to such work.