I keep an old PowerMac 7100 with Mac OS 8.6 on the hard drive on a shelf in the back of my shop, just for occasions when I need to read an old 800K floppy.
External USB floppy drives will not read 800K floppies (because the 800K capacity on what was really a 720K disk required a drive that would run at variable speeds. None of the external USB floppy drives will do that). If you have something like a beige G3 or a G3 All-in-one that has a built-in floppy disk (which will read the variable-speed floppies) you have to use it in OS 9, because Mac OS X does not support built-in floppies (there are a couple of hacks that were supposed to remedy this, but none of them ever really did much for me).