Chocolate bars - Actual shelflife vs expiration date
If we're referring to plain chocolate bars, I say go for it.  Plain chocolate (unsweetened, milk, or dark) lasts, if unopened, for years.  The most that will happen is that the outside turns whitish in color, but this does not affect taste or quality.  If there is any sort of filling, though, I, personally, would not eat it more than a month or two past the expiration date.