...the humble cupcake. Well-iced, preferably wtih the help of lots of toxic food colourings and sprinkles. And if you want to make absolutely sure that your dc has the most popular stall with the fastest-selling goods then stick a smartie on the top of all that icing and food colouring.
Yes, worriermum has done the research for you and after countless tedious school fairs and many hours spent making fussy goods for the fair, she can confirm the latest reserach findings. It seems no one can resist the plain but delicious cupcake...icing sugar and sponge cake win every time. (we ignore the bake-from-a-box brigade who give cupcakes a bad name..smug alpha-mummy baker emoticon needed here)