How accurately can you measure mass [weight] and volume ? 1 ml = 1 cubic centimeter, 1 cubic centimeter at room temperature = 1.0028 grams. If you have some to measure 2 volume of water, you can accurately determine the volume of the coin. You need something that allows a consistent max capacity , say the plastic top to a bottle, just larger in diameter of your item and deep enough to be filled above the item. The easiest way then is to place the cap on a scale, tare the scale, fill it to the top with water, and record the weight{1}. Empty the top, tare the scale , place item in the top and fill the top. Note the weight{2}. The weight {1} - weight {2} will be equal to the volume of the medal/coin . Just divide its weight by the volume and you will have the density of your item. But this works only for pure metals, as the density of alloys can be really complxt.

Bruce