Find a plain eraser, preferably white. The eraser must be large enough for you to draw a design that you can comfortably cut around.
Draw your design in pen on the eraser. Practice on a piece of paper before you draw the final design.
Chisel away the parts outside the design, using a V-shaped woodcarving tool. The more complicated and smaller your design, the harder it will be to cut accurately. Once you finish, the rubber stamp is ready to be dipped in ink and used.
Find a thin piece of foam, such as the container that chicken breasts or ground turkey come in, that will fit the design you have in mind. Clean the foam with soap and hot water and cut off the sides.
Draw your design on the flat, middle portion of the container.
Cut along the lines of your design to create your shape out of foam and remove the excess from around it. When you are done, all you will have is a piece of foam in the shape of your design.
Use a nail file or sandpaper to sand down any uneven edges on the foam.
Cut out a piece of cardboard from a cereal box. Using double-sided tape, stick the foam design to a piece of cardboard to finish the stamp.