For the parachute, take the trash bag and cut it directly in half so that there is still one opening, but the bag is half as tall.
Cut four strings to equal lengths and duct tape each one equally spaced out on the inside edge of the bag opening.
Then attach the four ends of the strings equally spaced out on the inside of the cut bottle, and the parachute is complete.
Fold up the parachute in a very small square in order to not cause friction during the separation, and place the chute inside the cut plastic bottle.
For the launch, fill up the in-tact plastic bottle about one third of the way with water, and lightly place the cut plastic bottle on the bottom of the in-tact plastic bottle.
Pump up the launch mechanism to fifty PSI, make sure mechanism is secure, and let it fly!
Rocket Procedure
Cut one of the two liter bottles in half, keeping the part with a cap, and cutting the bottom part off so that only a few inches are left on the bottom.
Fill the cut top half with newspaper, and shove the cut up bottom bottle into the top half, compressing the newspaper.
Cut out fins, and attach fins to the completely intact bottle, making sure to leave room for the launcher at the bottom.
Attach a nose cone to the cut up bottle by folding the thin plastic sheet from corner to corner.