"Something old" is the first line of a traditional rhyme that details what a bride should wear at her wedding for good luck:
Something old,
something new,
something borrowed,
something blue,
and a [silver] sixpence in her shoe.
The old item provides protection for the baby to come. The new item offers optimism for the future. The item borrowed from another happily married couple provides good luck. The colour blue is a sign of purity and fidelity. The sixpence — a British silver coin — is a symbol of prosperity or acts as a ward against evil done by frustrated suitors.