We don't know much about the Old Copper diet directly. In her book on the Old Copper Complex, Wonderful Power, Susan Martin relied mainly on upstreaming later archaeological sites and historic cultures in area to get an idea for what was likely on the menu. Her list includes trout, whitefish, sturgeon, maple sap, wild rice, berries, tubers, deer, moose, and bear as the major food sources. The Old Copper Complex is likely too early for intensive utilization of maple sugar. The more northerly cultures of the Old Complex Complex would have access the caribou which ranged further south at the time. Hickory nuts and walnuts were popular foods in contemporary cultures to the south, but viable ranges for these trees barely come up to the southern limits of the Old Copper Complex today and might not have done so at the time. Nuts became less important as food sources after the Archaic, so they don't show up as often in the later archaeological and historical contexts that Martin used.