If I expect to signal people (leading a class or trip) I carry the horn. The
Fox 40 lives in my PFD all the time.

I used to have a Storm whistle on a badge retainer--One of those things you
hang your ID badge on with the retractable line. After losing the second Storm
when the retainer came off the PFD, I gave up on that. I still have a third
Storm, but it is attached to my lunch dry bag.

YMMV, but the Fox 40 is small enough to leave dummy-corded in the PFD pocket.