Tada - homemade squeeze rocket launcher:
Small water bottle
Small straw (comes in a pack of 50-100 for ~$1 in most grocery stores)
Bigger straw (recycled from a McD's soda)
*Drill a hole, with similar size diameter as your straw, into the cap of the water bottle.
*Cut the small straw down to ~3 inches.
*Insert straw into newly made hole.
*Glue the straw into place (optional).
*Various size straws closed off completely on one end with a small sticker. (You can vary length/diameter, but the diameter of the rocket needs to be large enough to easily come off of the smaller straw with a squeeze of the bottle).
*Nerf-ish rockets (these too are fairly cheap - we found a pack at Fry's around Christmas that we've been using with our other rocket launchers too).
*The launcher works better with one quick hard squeeze.
*Plastic water bottles are poor quality plastic and deform really easily.
*You can blow into the straw to quickly reform the bottle (demonstrated in video below).
*I don't recommend gluing the cap onto the bottle since you might want to stick a long skinny to recover the bottle shape.
*Ultimately it takes 2 minutes to put together, so it's not worth getting frustrated over the bottle.
*Alter the length and diameters of the straw rockets being launched. Note the differences between the rockets.
*Decorate the straws being launched.
*Give the straws fins and wings. How does that change the flight of the rocket?
*Aim for a target.
*How high can you launch the rocket to the sky?
Here's a video of Big and Little J launching the rockets. It's hard to capture the flight of the rocket. The first launch was the Nerf-like rocket and the second was the straw: