I'm a fan of the Susato whistles. They are a good quality plastic whistle and you can buy them as a set of C, D, Bb at a discounted price.

Perfect to complement all of the most common Cajun accordion keys.

Being a plastic whistle, they are not subject to the issues found with "natural" whistles on camping trips, etc. They do cost more than the "cheap" plastic, whistles, but they play very well and are a good all-a-round instrument.

They play loud, stay in tune, and have a nice "chiff" if you want it.

That is my two cents.
DP