Liquid nitrogen is great for all kinds of physics demonstrations, and for just having some fun with. But be careful: If you are't trained to work with this stuff it is very easy to injure yourself with liquid nitrogen. Only follow these steps if you know what you are doing. Otherwise, this article is for educational purposes only.
Start the process to make your own liquid nitrogen by cutting off the top of the 2 liter coke bottle. Cut it a few inches down from the neck of the bottle at the widest point, so the bottle is still as tall as possible, but does not have a narrow opening.
Next, poke a series of small holes in the bottom and lower parts of the side of the smaller coke bottle using the scissors. Cut the top of the smaller coke bottle off the same as you did for the larger 2 liter coke bottle in Step 1. Place the smaller bottle inside the larger one.
Pack about three to four inches of dry ice around the smaller bottle inside the larger 2 liter bottle. Fill the larger 2 liter bottle with 99% isopropyl rubbing alcohol, pouring around the center smaller bottle.
Now, the liquid that enters the smaller bottle from the 2 liter will be similar to liquid nitrogen. You can test it by dipping a flower into liquid nitrogen in the center and then shattering the flower on a table top.