Step 18: Payloads steps 1,2,3
payloads are used to carry equipment such as altitude meters, accellerometers or even a slug (wierd, but the g-forces can kill it!)
cut the bottom off any size bottle.
cut two disks the same width as the bottle out of corregated plastic
cut a strip out of plastic the same width as the bottle but a little bit smaller in length than the bottle
Glue them together and when dry put your payload into the payload section of the rocket.