I pick up loose zipper pulls at various airport baggage carousels. They are usually lying where the rubber bumper meets the sliding metal plates. I've used plastic wire ties also but they usually last less than 6 trips before nothng but a nub is left. If it's an emergency, a large paper clip also does the trick. I like the sliding spring-loaded zipper mechanism that Costco put on their roll aboards, so replacement pulls can easily be added, but some of these spring-loaded mechanisms have already been torn apart on my bag.

-outoftown