The word “supplies”, as used in sections 50.760 to 50.790, means materials, equipment, contractual services, and shall be held and construed to include every article or thing, excluding utility services regulated under chapters 392 and 393, for which payment may by law be required to be made by the county, and including advertising and printing required to be done by the county. The term “purchase” includes the rental or leasing of any equipment, articles, or things.