What is traditionally worn on the left side while in formation?

Ribbons and medals are traditionally worn on the left side while in formation as a means of displaying personal achievements and honors in a manner that is readily visible and recognized by others. This leftside placement is consistent with military customs and regulations, which dictate that the left side of the uniform is the designated area for such insignia. It allows for uniformity and easy identification of service members' qualifications and accomplishments.

In contrast, hats generally serve a practical and functional purpose and do not carry personal achievements or recognitions, which is why they are not specific to a side in uniform regulations. Cuff links, while they can be part of a dress uniform, are not typically associated with formation settings and do not convey military honors. Belts are functional items that serve to hold up the uniform trousers and do not display any awards or decorum, hence do not have the same significance in the context of formation.