DISCLAIMER: Though this whistle is ear-splittingly loud when configured properly, I have not tested it in a survival situation. Please use your own judgment on whether your end product is good enough for a real survival situation, if that is its intended use. If it isn't good enough for that, please consider shelling out the money for a factory-made whistle.
Here are some pages I viewed which were very helpful in learning about the construction of whistles:
Step 1: Materials
--small piece of sandpaper
--Papermate Eagle ballpoint pen
--it is quite possible there are other pens which will also work; I have selected this one for several qualities. First, there is no hole in the barrel of the pen--for some reason many ballpoint pens have a tiny round hole somewhere on it. Second, the ink cartridge is easily removed with your fingers. Third, the end piece is a separate piece that can pop out.
Step 2: Remove the Ink Cartridge From the Pen
Step 3: Mark and Cut Pen Barrel
Step 4: Sand the Cut End
Step 5: Mark and Cut at the Original End
Step 6: Grip and Squeeze Original End
Step 7: Insert End Cap Into Mini-pen Barrel
Step 8: Cut a Line (window) Perpendicular to Mini-pen Barrel
Step 9: Cut a Wedge (lip) at About 45 Degree Angle
Step 10: Cut Side of Barrel to the Bottom, to Create an Air Passage
If possible, remove the end cap. You can sometimes remove it at this point by using the point of the lid, or some other pointy tool. Be careful, though, as there is the possibility of snapping off the cut end of your barrel. If you cannot remove the end cap, that is fine. You can do this step either way.
If you can remove the end cap, you can use your scissors to cut just over a third of the middle of your barrel end out, making a mushroom shape when looking at it straight down. If you cannot remove the cap, use your knife to shave down that same area. This is part one of the windway.
Step 11: Grip and Sand End Cap
Step 12: Insert the End Cap Into End of Barrel
Step 13: Cut a Mouthpiece Section Off the Original Middle Section
Step 14: Cut Mouthpiece Down Middle of One Side
Step 15: Cut the Corners Off One Side of the Mouthpiece
Step 16: Place the Mouthpiece on the End
Step 17: Troubleshooting Ideas
--You can move it forward and backwards to figure out the area which produces the loudest tone.
Plugging the end
--Some whistles end up being loudest when you plug the other end with your finger, some when you don't plug the end.
--Sometimes it helps to hold the mouthpiece tightly while you blow your whistle. If that's the case, when you are satisfied with your configuration you can consider gluing the mouthpiece into place.
Try the above in several different configurations to find the loudest whistle. If none of the above work, you can try the next two steps.
Cutting/sanding your fipple
--If you've tried the above, you can try sanding down the end cap a bit more, and adjusting a bit the sides of the cut barrel portion. If you can't blow the whistle at all, this is definitely the area you need to fix.
Cutting lip/hole larger
--If you've tried the other things, you can try cutting your angle differently on the lip.
Step 18: Cut Ink Cartridge
Step 19: Place Ink Cartridge in Mini-pen, and You're Done!
If desired, you should have enough room to also place the cap on the pen. Currently this takes up extra valuable space in the Altoids tin, but I will work on turning the cap into a small-game trapping mechanism to make it earn its place.
Consider adding instructions to the barrel of the mini-pen to explain about taking out the ink cartridge before use. Some pens will still work nicely with the ink cartridge in place, but most won't. In order to use the whistle you will need to remove the ink cartridge temporarily.
Now your whistle pen is complete and ready for your tins!