Flint points, obsidian, buffalo hides, salt, pearls, shells and (as mentioned by T.E.D.) copper were among item traded by Native Americans before Europeans arrived. That said, trade in North America prior to European contact varied greatly in its extent and volume, depending on area and epoch.
From Trade Among Tribes: Commerce on the Plains before Europeans Arrived by Samuel Western (Wyoming State Historical Society), our two main sources of this trade come from archaeology and from accounts of the first European traders to reach various regions.
From archaeology,
Indians of the southern and northern Plains traded with each other for
thousands of years. Flint points 13,000 years old, chiseled from the
Texas quarries, have been found in eastern New Mexico. Quarried stone
from the Obsidian Cliffs near Mammoth Hot Springs, Wyo. in Yellowstone
Park, traveled to the the Ohio River Valley around 100-350 CE.
.....
Archeological artifacts do suggest...that native-to-native trade
expanded over time. Emory Dean Keoke and Kay Marie Porterfield,
authors of the Encyclopedia of American Indian Contributions to the
World, say that the Hohokam tribe, centered in present day Arizona,
traded seashells, which they had acquired from the Mojave tribe, for
buffalo hides from various southern Plains tribes. “By between 500 and
200 B.C., North American Indians had established a vital network of
trade.”
Also,
A research team including Matthew Sanger, assistant professor of
anthropology at Binghamton University, State University at New York,
has found a copper band that indicates ancient Native Americans
engaged in extensive trade networks spanning far greater distances
than what has been previously thought.
The researchers found that the band was made from copper that
originated in the Great Lakes region, more than 1,500 km away. Copper
sources each have their own unique chemical makeup, including very
small amounts of trace elements. As such, archaeologists can match
manufactured objects to their sources by comparing their chemical
signatures,...
Copper was also traded in the Southeast (among other regions), along with salt, pearls and probably ceramics. Many kinds of stones / minerals (sandstone, soapstone, chert, galena etc.) were also traded, both before and after their transformation into status items and / or weapons.
On food (other than corn / maize), the sources are less definite. On the one hand,
Because North America lacked an animal that could be domesticated for
draft purposes and was wanting for any other efficient means of
regional and continental transportation as well as an organized market
system, the people of this continent did not trade food products to
any great extent.
Source: 'Chapter 1' in Jonathan E. Ericson & Timothy G. Baugh (eds), 'Prehistoric Exchange Systems in North America'
On the other hand, it is impossible to rule out local exchange of foodstuff. Michael B. Stewart, in Late Archaic through Late Woodland Exchange in the
Middle Atlantic Region (in Ericson & Baugh) states:
Foodstuffs and artifacts fashioned from organic materials are poorly
preserved in the archaeological record of the region, their absence
serving to remind us that we are seeing only a part of the whole
picture of Native American material culture.
Nonetheless, Susan C. Vehnik and Timothy G. Baugh in Prehistoric Plains Trade (in Ericson & Baugh) cite Henning (1983a) as suggesting that there was some trade in bison hides and dried meat in the period 800 to 1200 AD, while trade in 'bison products' is mentioned in relation to the Southwestern Pueblo in the period up to 1650. Given that Native Americans could and did hunt bison before they had horses, the trade in items derived from these hunts is at least plausible.
Accounts of early European traders are also a valuable source of information as
artists who visited the upper Missouri and Rocky Mountains in the
1830s noticed tribes hanging onto traditions or only selectively using
European goods.
The addition of European goods did not suddenly change Native American trading habits, although it should also be pointed out that tribes sometimes acquired European goods from other tribes (i.e. without meeting Europeans themselves). Tribes
tapped Wyoming’s abundant natural resources for desired trade goods:
quartzite or obsidian for knives, scrapers and arrowheads; buffalo for
robes, dried meat, pemmican and hides; soapstone for bowls; elk or
deer for tanned hides; and horn, particularly from the bighorn sheep,
for making bows, which were highly desired.

"Trade links among northern Plains tribes about 1775, before the arrival of Europeans. Courtesy W. Raymond Wood." Source: WyoHistory.org
Western notes that:
The Shoshone, it seems, traded with everyone, including northwest and
southwest tribes. Other Rocky Mountain and central Plains tribes also
took goods to the Missouri River valley to trade for corn, pumpkin,
squash and native-grown tobacco (Nicotiana quadrivalvis, Pursh)...
Over time, European goods were traded alongside / in exchange for local products:
Corn also appealed to former woodland tribes. “For the Sioux, corn was
more important than blood,” says James P. Ronda, professor of Western
American History at the University of Tulsa. In August, “as in every
other late summer and early fall, Sioux bands flocked to the Arikara
towns, bringing meat, fat, and hides from the plains and
European-manufactured goods from the Dakota Rendezvous.”