If you're baking a cake for a movie buff, you might like a bag of popcorn to be the centerpiece of your design. Real popcorn will quickly go stale, so you'll want to construct a fake variety.
Take a piece of fondant and roll it into small balls, then use a knife to cut several slits in each ball and pinch together to form the distinctive popcorn shape. Either use pale yellow fondant or paint with yellow food coloring. For extra authenticity, sprinkle with Luster Dust.
Take a packet of mini marshmallows and cut an X shape on top of each one with a slightly heated knife, then squeeze the bottom slightly and color using food coloring spray. To add "butter," drip on bright yellow frosting.
Make a batch of very thick buttercream and pipe popcorn shapes onto a sheet of greaseproof paper. Allow to harden. For added authenticity, dot with dark brown food coloring.