Coin Boxes have an identical appearance to a ? Block. Like the Propeller Box, they can be worn by Mario over his head. It cannot be taken off unless he hits an enemy. If Mario makes it to the Flagpole with the Coin Box, it disappears and a 1-Up is received. While inside a Coin Box, infinite coins will pop out from it while he is moving.
In New Super Mario Bros. 2, similar objects known as Gold Blocks appear which give Mario coins at a much faster rate than the Coin Boxes. Unlike Coin Boxes, however, a Gold Block will disappear once 100 coins have been collected from it.