> You'll go to the picnic, won't you! Yes : not to ; No: go
> ....., 不是吗？ 是的，我不去； 不，我去。 [/quote]

A: "You'll go to the picnic, won't you?"
B: "Yes, I will."

You can't say "Yes, I won't". That's a common mistake some Chinese make, because the Chinese language allows you to have one positive and one negative part in the answering  sentence.