Here are a couple of things I've made for bake sales & sold pretty fast:

Jelly Roll (using your favorite filling)

White cake, with white icing, coconut & a cherry on top (this is a fast seller)

Chocolate Chip Cookie pizza....drizzled lightly with chocolate glaze

Cookie Hamburgers.....These are a little time-consuming, but VERY cute. Vanilla wafers are the "buns"; one half of an Oreo or other kind of chocolate cookie = "the meat patty"; green tinted coconut is the "lettuce"; & then get some yellow cake decorating gel or the decorating icing in a tube for the "mustard" & red for "tomato" slices. Spread just a little honey on the top of one vanilla wafers (the top "bun") & sprinkle just a few sesame seeds or poppy seeds on top. When I made these I only made a dozen. These, too, sold very quickly.

Good luck with your bake sale.