Found this stuff on the web. I thought it better explained what the phrase "Don't take any wooden nickels!" means:

First recorded in about 1915, this expression was originally a warning from friends and relatives to rubes leaving the sticks in the great migration from rural areas to the big cities at the turn of the century. It was a humorous adjuration meaning beware of those city slickers, for no real wooden nickels were ever counterfeited - they would have cost more to make than they'd have been worth. Ironically, country boys were the ones who possibly did succeed in passing off wooden objects as the real thing. Yankee peddlers as early as 1825 allegedly sold wooden nutmegs, which cost manufacturers a quarter of a cent apiece mixed in with lots of real nutmegs worth four cents each." From "Encyclopedia of Word and Phrase Origins" by Robert Hendrickson (Facts on File, New York, 1997).

: : A second source says, the expression means: "Don't let yourself be cheated or ripped off. Originated in the United States in the 1920s and 1930s. Money that has no real value is sometimes called 'wooden'.Probably stories about wooden nutmegs, wooden hams, and wooden pumpkin seeds contributed to the later use of the phrase 'wooden nickels' in American or even to the use of 'wooden rubles' in Russia." From "Random House Dictionary of Popular Proverbs and Sayings" by Gregory Y. Titelman (Random House, New York, 1996).

: : Another source adds: "The United States minted five-cent pieces from the earliest days of the Union, but they were not known as nickels until 1866, because in that year the first five-cent coins containing nickel were minted. The practice of making commemorative tokens out of wood as centennial souvenirs developed and we assume that wooden nickels actually were made during the nineteenth century for this purpose. Frequently such coins are accepted as legal tender while the celebration is in progress, but of course they cease to have value when the show is over. So the expression 'Don't take any wooden nickels' became the popular equivalent of 'Don't be a sucker.'." From "Morris Dictionary of Word and Phrase Origins" by William and Mary Morris (HarperCollins, New York, 1977, 1988).