I've heard a lot of these!
My Irish grandmother warned me about opals, too... saying that they should only be worn if they are your birthstone OR if they were given to you on a special occasion; she would say that buying an opal for yourself would bring bad luck.
(Sad for me... I absolutely LOVE opals, but no one has ever gifted me one!!)
I've heard about not wearing pearls until you're married - and I've warned my teenage sister about this because she wears pearl earrings every day - but she argues that it goes against everything that a "Southern girl" believes and wears them, anyway.
I've heard about the horseshoe jewelry needing to be worn as: U ...and not upside-down, because the shoe should form a "bowl" to hold good luck, and if turned upside-down the luck will spill out.
I've heard that elephant jewelry should always feature an elephant whose trunk is lifted up, because this is lucky. Elephant jewelry that features an elephant with the trunk pointed downward should be avoided.
I've also heard from Italian relatives that Evil Eye jewelry should only be worn if it was gifted to you, as the love in the gift protects you. They said that if you purchase the eye jewelry for yourself, it backfires and turns the evil eye on you instead of protecting you... something about selfishness?
I've also heard that heirloom wedding or engagement rings should not be handed down to new brides/grooms if the marriage was not a happy one, or if the past wearers divorced, as that would bring the negativity from the failed marriage into the new marriage... thereby dooming the new union.
And yes, I've heard that gifting wallets or handbags should include a penny or a dollar inside of the wallet or purse... something about gifting an empty wallet will mean that it will always be empty, but gifting a wallet with money means that it will always contain money.
I'm sure there are so many more that I'm forgetting.... but my family (Irish/Italian/Polish) was always very superstitious!