I used three cake mixes and a 12″ and 8″ rounds for this Nemo cake. I bought the food coloring at the grocery store in the neon colors and the fluffy white frosting by Betty Crocker (I think) and believe it or not that’s how I got that blue color.
I went to the Disney store and bought the Nemo figurine package for the characters. Those are the only inedible objects. The little fish were the baby goldfish crackers (they are smaller than the regular ones) multi-colored strands of fruit rollup for the seaweed and the rocks are jelly-bean brand jelly beans. I used the speckled ones because the look most like rocks.
I got the inspiration just by looking online and putting my own twist on things.