The powers, functions, rights, privileges and immunities of the departments described in Article III, Section 2, and of any other departments, commissions and boards created by ordinance pursuant to Article III, Section 2, or otherwise, shall be defined by the governing body of the City within the limits of this Charter and the general laws of the State. Supplies and personnel for the various departments, commissions and boards shall be provided by the City Manager within the limits of the appropriations therefor. Except as expressly provided in this Charter or in the general law of the State, no full-time officer or employee of the City may hold any other office or position (except an honorary one) with the City, the State or the United States, or any department, commission, board or instrumentality of any thereof; provided, however, that (a) the City Clerk may also act as Chief Clerk of the Accounting and Treasury Department; (b) the City Manager may assign any City employee to perform services for two or more City departments, commissions and bureaus; (c) any City official or employee may also act as a volunteer fireman; and (d) if and so long as the governing body of the City so directs, the City Manager shall perform the functions and have the powers, duties and immunities of the head of the Health Department, the Public Works Department and any other department, board or commission created by ordinance pursuant to Article III, Section 2.