Your button is a yankee Infantry Officer's button. Although that spefific emblem was in service from 1854 though early-1874. your button's completely blank brass back with a "non-soldered" (flexible) thread-loop mean it was made during the civil war years, when the demand for vast quantities of those buttons caused some manufacturers to save manufacturing time and cost by not bothering to put a maker's-mark (called a "backmark") on their products.
At the extreme left in your group photo, I see an iron dinner-knife, whose wooden or bone handle has rotted away. That specific type dates mostly from the 1800s.
At the upper left corner in the group photo, I see what may be a civil war era brass or copper bullet cartridge casing, missing the bullet. We'll need precise measurements and close-up photos of it to be sure whether or not it is indeed a cartridge casing.
You asked about dollar-value. The civil war yankee Infantry Officer's button doesn't seem to have much (if any) of its gold plating, but is otherwise reasonably intact. Not showing gold plating (which most of that type do show), it would sell for about $15 at a civil war relic show here in Virginia. Might bring a bit more in other areas of the country.
