Honestly, as a backup, any of those supermarket earbuds you can get for like $10. I remember when I was in college and my pair of Porta Pro’s snapped, some ultra cheap Koss KEB in ear’s that the college bookstore sold were a lifesaver while I waited for my warranty Porta Pro’s. They sounded good enough and blocked noise, and for a music lover like me literally anything would be better than no music at all.