I love this stuff:
Depending on the tribe and the time period, there are many "detectable" items. knife blades, beads (even very old Venetian beads have a fair bit of mineral in them), needles. In other words all the trade items of metal, incuding the cooking utensils mentioned earlier. There are also the metal parts of muskets, balls, bullets, axes, tiny bells (many indian tribes loved bells) and medals from the Great White father in the great White House, which were handed out like bus tokens. Also coins that have holes drilled in them for earrings and necklaces and general ornamentation. Southwestern Indians got their metal from the Spanish, and so there are iron and brass and silver trinkets.
Just takes a little research about the tribes in the area you are in, and good hunting.
Cheers
Deb