The modern gifting theme for your twenty-fourth wedding anniversary is musical instruments! As Shakespeare once said: "If music be the food of love, play on."
If you're other half already plays music, it could be a good idea to upgrade their instrument, or you could buy an instrument that they've always wanted to play, such as the piano or a guitar.
If your partner is the type who prefers listening to the sweet sound of music rather than playing it, you could bend the rules slightly and go for music related gifts. You could opt for high quality headphones or speakers to enhance their listening experiences, or pick a favourite piece of music that holds dear memories of your times together.