bring both just in case event safety manager will check what's the best option, the PFD is the non negotiable item on the list, the others just practical really, you can get sunstroke/dehydrated and feet cut to pieces if you wish.
As mentioned you can get a long way from home, depends on where you are we can be talking kilometres! So it can be hard to see anyone floating about out the back, could be a while before you are reached, nice if you can kick back with something to float you and enjoy the serenity!
If you don't like the whistle you can bring a flute or clarinet if you like, so long as its in tune we don't really mind!