It's easy to turn a piece of plastic candy wrap into an improvised loud whistle.
For those who don't know:
-It has to be a paper or plastic. You can't do this with fabrics. Just take a wrap of at least 1x1 inch. Bigger is fine, it doesn't matter.
-Hold a size of the wrap with your index and pointing finger. They must hold at least a centimeter apart and pulled apart. Avoid destroying it.
-Then blow at the centimeter gap and annoy the crap out of people.
-The bigger the gap, the lower pitch it produces.
Ah yeah. I used to do this using thumbs and the meaty part of the hand and some grass.