You can buy gold leaf kits for as little as $5 to $10 at Michaels or other craft stores.
To use them you just paint the glue onto the areas you want gold, and then when dry, gently press the gold leaf onto the area. Since the gold leaf will only stick to the glue, you just brush away the excess.
Should work fine for something like a leather book cover, but I couldn't vouch for how well it will last on clothing and such.