I make a lot of ginormous half-sheet cakes. So does Costco. Pretty sure mine taste better (although they do have some yummy filling options). I realized I didn't have any posted here, so I dug up a picture of one made for a graduate from a master's program.
The cake was chocolate. Accents are mini Snickers candies. And I believe there were chopped up Snickers incorporated into the filling. Take that, Costco.