What you'll need:
Double-sided Scotch tape
Download and print the gel template PDF from step 1. It will fit on a standard sheet of copy paper. The photographer's gel can be purchased at photography and filmmaking stores or online. If you're making Blinky, Pinky, Inky or Clyde you'll need two gels: One for the blue pupils and one for the gel template to color the paper cylinder (red for Blinky, pink for Pinky, aqua blue for Inky and yellow for Clyde). If you're making "don't eat me!" (when Pac-Man eats one of those big pellets) you only need the one blue gel (the same color used to make the pupils for the other ghosts).
The shops that sell photographer's gels will often offer gel sample booklets as well. These booklets are very cheap if not free. The gel samples inside are large enough to make the blue pupils from.
Tape the template paper to the gel so that the template lies face-up with the gel on top of it (second picture). You may want to place several pieces of double-sided scotch tape between the paper and the gel to help hold it in place.
For the next part where you use the compass and needle (third picture), you could simply use a pair of scissors or free-hand it with the Xacto knife, instead. But the method I describe below makes much cleaner cuts.
Now take the drawing compass and the needle. Remove the pencil lead from the compass and replace it with the needle. You may need to wrap tape around the needle so that the compass can grab it. A sewing machine needle may work better because it's thicker. You'll use the compass to cut out the two circular shapes on either end of the template as well as the eye holes. You'll also need the Xacto knife and ruler to cut out the rest.
Choose one of the large circles and place the compass pin on the center dot. Set the needle on the other arm on the circle's outline. Swing the compass back and forth and the needle will cut through the gel, creating a perfect circular cut.
DO NOT do a full 360 degree cut. Leave the part that connects to the rectangular shape intact so that the whole thing stays in one piece. Put some tape over that spot to stop you from cutting there.
Now let's cut out the eye holes. Before cutting the half circles, take the Xacto knife and ruler and cut the straight lines between each half circle. Now take the compass and cut out the half circles. Once that's done, use the Xacto knife and ruler to cut the remaining straight lines.