I do a huge local craft show in my town. Did it last year and made 24 dozen cupcakes thinking that was a HUGE amount of cupcakes.....but sold out by NOON! I couldn't believe it! People were coming up to me asking to take whatever I had left! So I think this year we'll plan on more obviously
I would just pick a number that you KNOW you can handle. Or maybe think about how much money you know you NEED to make back to cover your costs (did you pay for a table/registration etc) and make at the very LEAST the amount of product that it will take for you to break even....and then go over that so that you can make product.
For us, doing this craft show last year was more about getting our name out there, (we had brochures, a slide show etc) to get more people to see what we do and order our cakes, then it was about making LOADS AND LOADS of money... know what I mean?