Yo, Kevin -- Wow. Great. Keep it safe. It's valuable. Handle it with white cotton gloves, only by the edges. Store it away from moisture and chemicals. Don't put it in a plastic bag, because they contain chemicals which will ruin the surfaces. Keep it separate from other coins.
I am pretty sure you have a 'brockage error' coin. It is hard to tell from your pictures, but that's what it looks like at first glance. Find a coin dealer in your area, a person you trust. He or she should be able to tell you about your coin.
For an explanation of 'brockage' and approximate values, see this page:
Yo, Kevin -- You have a lot of nice coins. Please invest a little time to learn how to best store them. If there is a coin shop in your area, pay them a visit. Do not clean your coin. Handle it with extreme care ... touch only the edges.
This "coin" is not really a coin, but a medal. These are often called "so called dollars" because they are the size of a silver dollar, but they have no denomination.
Your medal is valuable. It came from the 1915 Panama Pacific Exposition in San Fransisco. The one in my picture below sold for $400 US dollars during a recent auction. Below is the description of the medal from that auction.
UNITED STATES. Panama-Pacific International Exposition, 1915. Official Medal. San Francisco. Silver "So Called Dollar" 30.18 gm. 38 mm. The official silver dollar from the exposition. Winged Mercury opening the Panama Canal locks; the Argo (from Jason and the Argonaughts, a symbol of navigation) sailing through; "ON! SAIL ON! in small letters below left; TO COMMEMORATE THE OPENING OF THE PANAMA CANAL MCMXV around / Two female figures representing the hemispheres reaching across a globe holding cornucopias, a seagull below; PANAMA PACIFIC INTERNATIONAL EXPOSITION SAN FRANCISCO CALIFORNIA MCMXV around. HK 399. Uncirculated; lustrous with hints of light toning.