Assembled cupcakes to form a caterpillar makes for a really easy, simple and creative birthday cake.
Get the instructions here:
http://cococakecupcakes.blogspot.com/2009/03/hungry-caterpillar-cupcake-party-train.html
Cupcake toppers are also a cute way to go.
(Original source was compromised.)
The backs of M&Ms make for an even easier design as shown by boy mama teacher mama.
Get the instructions here:
http://boymamateachermama.com/2012/09/29/boy-mama-the-very-hungry-caterpillar-a-puzzle/