These are used to carry goods that require shelter from the elements but don't need to be kept at a certain temperature. They're made of steel with a wood or plywood floor.
You can upgrade to a ‘food quality' general container for items like canned or dry foodstuffs. Forty foot containers have the same characteristics as twenty foots with the obvious advantage of being twice and long and holding twice as much volume. Ideal for when you have a lot of cargo.