Yes, we know this is stating the obvious a little. Everybody knows that old coins are worth money, and everybody knows that collecting old coin is quite a popular hobby. What the majority of people don't realize is that coins don't have to be all that old in order to have a value beyond what's printed on them. You also may not completely comprehend the true value of some old coins - we're talking $200,000 for one coin in extreme circumstances.
If you have American coins which are over 200 years old, and they're in good condition, get them valued immediately. After you've had them valued, get them insured, and then get them somewhere safe so that nobody else ever touches them. If that sounds like too much effort, just get them sold and spend the next couple of years living off the profits. Vintage coins can make you life-changing money.