Whenever we are about to go have some family fun time and do something my 4 year old daughter is really excited to do she decides to throw a fit about something ridiculous right before we leave (ex. won't eat breakfast, won't get dressed, cries about her coat not fitting right) that at times causes us to cancel our plans completely. I don't know what to do about this, I have tried taking privileges away but sometimes it seems like she craves this unhappiness? any advice?

Maybe too much excitment overwhelming her and leading to a melt down...and if she's become used to you withdrawing treats as a result she may be using it as a form of control over feelings that are more than she can cope with (rather than any wish to be unhappy). I would continue to go regardless or this may become a self esteem issue and lead to self destructive behaviour...and the more she experiences it in a positive way the faster she will be able to cope with the feelings.

My daughter always, without fail, sulks just before a big day out,and I remember doing it myself as a kid, I don't think its an uncommon problem.

Don't cancel anything. That's painful for her and she learns to resent you. She cannot control this and it is natural. Learn to validate her feelings and support her through her excitement. She can skip breakfast, it won't hurt her one time. Go with her to her room and join her on her confusion about getting dressed. She is so excited, she wants to look perfect.

Validate her feelings and also let her know that she looks great no matter what she wears and that you love her. Learn to go with, not against her and she will
learn life lessons on her own with your love and support.

Like I said before, I have learned these skills from books and workshops. I attended teleclasses, read, listen to CDs... Parenting has to be learned. It is the hardest job on earth and we need to learn.
I mention books I like in other posts but choose whatever fits your aspirations.