Believe or not a trip to the bank can be a good source. When I go to do normal transactions I ask if they have any half dollars. Because I still get good hits on them from time to time. My second choice is the nickels because not many people know about the 42 to 45 war nickels. I haven't much luck with the dimes and quarters as most of them has been removed from circulation. I hit a mother load once when I bought a friends coin jar dollar for dollar because when most people discard their change in their favorite coin jar they don't look at them.
And don't get me started on electronics especially computers. Some older models have gold and silver in their circuitry. For this you will need a metal test kit that can be obtained from a jeweler or hobby shop.
But if you are gonna actively raid the attic, so to speak, you need to widen the net and that's where you find some really valuable goodies.
I have found discarded out of print books that I sold for 80.00. Some of the decorative wall plates are trimmed in 24kt gold, old style tea kettles, old letters, maps, calendars and comic books. I could go on and on.