buy real constitutional money: pre 1964 u.s. minted coins. they were made to exact tolerances for weight and metal content, are very difficult to fake, and are the most recognized throughout the world. also, may carry additional numismatic value. become best friends with your local coin shop owner. try to pay as close to spot price as possible. Silver eagles would be the next best thing, but technically they are not real money, only just a 'token'.