Let's see...
Airbrush (I use a Badger brand with a double action trigger - it controls air pressure and paint flow).There are probably better or worse ones out there. This is the only one I ever owned, and I didn't pick it out.
Paint
Paper (from my sketch book)
Pencil (to draw the design on the paper)
Xacto Knife to cut the design out of the paper (and turn it into what's called a "mask.")
Spray glue (to spray the back of the mask so it sticks to the shirt)
Tweezers (to grab the small pieces of the mask - like the teeth and eye)
Shield (WTF?!!) - Helpful for making wierd curves and shading. You don't have to buy one. You can make your own out of paper.
Beer