USB sticks, USB pocket hard disks, and SD/CF card readers all work great under OS 9. While you're at it - if you have USB: you can skip Zip. If your systems (or one of your bridge machines) have USB, they'll be running 8.1 or newer and can use HFS+ - just format your data transfer device with HFS+. Zip drives themselves work unassisted in the newest OSes and the only assistance you really need to use Floppy/Zip/MO/MD-DATA/Jaz/Orb/SyJet/literally-USB-sticks to transfer data is that both OSes involved need to speak a common filesystem. If HFS works with a floppy drive it will with a Zip drive. Neither OS needs anything extra to get to that point. It was mentioned but just as a reminder, 8.6 and 9 can use HFS+ and I believe they can even format floppy diskettes that way.

This applies whether you're doing networking or physical media. Strategizing on what those bridges are can help reduce how many of them there are and how well things work. We're getting to the point where having one or more bridge is more and more important.

How to format a floppy disk in mac