When I carry my 642, I usually carry a single Bianchi speed strip with 6 extra rounds. I have a couple of Safariland round speedloaders for it but they don't work with the standard grips, which I like otherwise.
Yeah, I have no illusions that I'd ever be reloading from that speed strip in a combat situation but it's so small that I figure why not. Doesn't hurt anything to have it along.