A lid includes a cover plate and at least one date display device. The cover plate includes at least one mounting area having a plurality of through holes. The date display device includes a plurality of digital display units each having a plurality of flexible protruding membranes to form a digit pattern. The protruding membranes are able to be selectively bent upward or downward to change the digit pattern. Each flexible protruding membrane is foldedly connected to the mounting area, covers a respective through hole, and is convertible between a protruding configuration that protrudes upward from the respective through hole and an indenting configuration that indents downward from the respective through hole.