The rules for suitcases vary depending on the mode of travel and specific regulations set by airlines, trains, or other transportation authorities. Generally, it is essential to adhere to size and weight restrictions imposed by the carrier. Carry-on bags typically have size limits and restrictions on liquids and prohibited items. Checked luggage may have weight limits and rules regarding fragile or valuable items. It's crucial to check the specific guidelines of the transportation provider before packing to ensure compliance with their rules and regulations.