What you need: Invisible ink, $3/bottle; Mini UV Light, $6
Risk level: High
To pull this off, you will have to know exactly where you will be sitting during your exam. If you can secure that, the rest is relatively easy. Using the invisible ink, write your cheats on your desk the night before the exam. You want to make sure you write it after the cleaning crew has made its rounds. On test day, whip out a mini UV light (preferably one that connects to your keychain) and read your notes. Or, you can write your notes on a piece of paper using invisible ink and bring with you to the exam. Whichever is easier for you, homie.