You will need:
Gatorade (a light-colored flavor would be best since it won't stain the cells.)
Small, clear plastic cups
Rubbing alcohol (put the container in your freezer for a little bit, it needs to be very cold.)
Liquid dish detergent
A Straw or Coffee Stirrer
An eye dropper (if you have one...otherwise, you could use a straw and your finger)
Have your scientist swish Gatorade in their mouth for at least 30-45 seconds (don't swallow) and then spit it out into one of the clear plastic cups. It helps if they can sort of bite on the insides of their cheeks a little bit, but don't bite hard! You don't want them to bleed, you just want to slough off plenty of cheek cells.
Now, drop two drops of dish detergent into the cup with the Gatorade spit. Gently stir with the straw for 2-3 minutes. Please stir carefully, trying not to create bubbles. The detergent will break down the cell membranes (lipids - fats and proteins) and the same way it breaks down the grease on your dishes.
Next, very carefully pour 2-3 teaspoons of cold alcohol into the cup with your Gatorade/cheek cell solution...pouring it slowly down the side of the cup, not dumping it directly in. DO NOT STIR THIS!
Leave the cup standing for about 5 minutes, but watch! You will see white clumps begin to form. This is YOUR DNA! Pretty cool.