This "School Bus" cake was a cinch! I baked 2 cakes in a bread pan, layered them and then frosted it adding vanilla cookies and donuts. You can use licorice and m&m's for more detailed decorating.
My "Lego" cake, I'm certainly no pro at this, but was delighted to see it somewhat resembled blocks. You can use any cake mix, bake it in a bread pan, then frost it. I actually made the circles out of frosting, then froze them before placing them onto the cakes.