I did a local market last year, well only for 3 Fridays. Here are some of the things that I learned:
1. Most of the people wanted the basic Chocolate and Vanilla Cupcakes, especially the kids.
2. The heat was HORRIBLE! I am in NY and we had 90 degree weather on the days I was there. We were on a black topped parking lot. I have a tent with sides for protection and shade. If you are using a frosting that is not made for the heat, be prepared. The first week I had chocolate with Chocolate frosting. They were selling well but not fast enough. The frosting melted on about 2 dozen of them so obviously I couldn't sell them. What I did the follow week was brought a cooler filled with ice and kept frosting in it ready to frost the cupcakes. Then I also use the under the bed totes to transport the cupcakes. I double up the totes and put ice between the layers to work as a cooler for them.
3. I used a covered cake display to show one of each flavor of cupcake available. I usually had about 4-5 choices.
4. Items such as Whoopie Pies sold like crazy because they were individual and easy to eat.
5. Make sure to have bags to put your containers in. The more convenient it is for the customer to carry, the more likely they will buy something.
I did really well the first week but then it slowed down after. It wasn't worth my time or the money to go to it. That being said, I am trying another one this summer that is MUCH more popular and VERY busy. I will try it and see how it works. Luckily for this one you only pay as you go. No season contract. I am willing to try things a few times. If they work than great, if not then I learned something. Good luck and I hope it turns out well for you!