Answer: A very easy to make rocket made from a drinking straw, and launched using air pressure.
Almost everyone will be able to make this, it does not require any hard-to-find items, but also can it be made in very little time. Therefore will the rockets themselves be very easy to mass produce.
They will fly HIGH up in the air, and then land on the ground, completely safe!
Okay let's get started!
Step 1: Gathering materials
You will need to print following document to continue, though:
Download this .doc!
The rest of the materials are descriped in the picture.
Step 2: Making the rocket
Put a dot of hot glue in one end of the straw making sure it's air tight.
Step 3: Attaching fins
Then fold and glue the fins together. Stippled lines means "fold backwards", whereas straight lines means the opposite.
You can use hot glue to glue the fins together, but I find that white glue (Elmer's glue or wood glue) works well.
Then glue the backside (the white side) and attach it around the straw, approximately 1-1.5 cm from the open end of the straw.
Step 4: Launch it!
Now for launching it:
Insert it all the way down in the nozzle of the bike pump, and give the bike pump a good, fast pump! Now enjoy your small flying rockets...
I had my rockets to go as high as ~10 metres!
Don't forget goggles, you don't want the rocket in your, or everyone else's eyes.
Thanks to Peter Hald for inspiration.