Two nine-inch round cakes. Cakes made from scratch will be denser and stronger than a cake mix, but you love the Duncan Hines don't you -- just be forewarned that the time you save using a mix will be spent cursing during the frosting crumb coat.
Two batches of frosting. We did a butter cream with 50/50 butter/vegetable shortening. Die one batch green. Keep 1/2 of the second batch white and die 1/2 blue.
Rolled fondant. We don't know what this stuff is, but we were darn sure we weren't going to make it. Found some multi-colored fondant at Michael's, a big box craft store. Buy the non-stick mini rolling pin while you are at it.
Decorations: cinnamon red hot candies for the eyes, candy corn for the tail spikes, chocolate chips for toenails, and toasted coconut for the prehistoric grass.
One cardboard cake board, half-sheet size.
Frosting pipe tips and bags. Use a star tip. Yes, this makes a difference, so don't skimp here. Really.
A partner. Not required, but could speed things up during frosting or at least help pass the time.