I get this question all the time: "what do I need to bring with me for our meeting?" Really, its simple.
The most important thing is a pretty solid knowledge of what you're willing to spend. Events can get expensive, and its good for everyone to know where you stand. Where is that line when you will become uncomfortable with costs? Money causes lots of trouble for folks, its easier to avoid arguments and surprises if you have already had a conversation about your budget.
It seems a little obvious. It happens all the time. Know where you stand and stick to it. I pride myself on finding ways to cut down costs so that you can get what you want. I have relationships with local vendors for this purpose; to make things easier on you!
You should also bring with you a "feel" for your day. Is it formal? Casual? Modern? Is it a large group of family and friends, or do you prefer something much more intimate? The usual comment I receive is "I just want people to have fun". That's great! What does that mean to you? Sometimes its getting people up on the dance floor, and sometimes that means lots of nooks and crannies for your guests to socialize. Its helpful if you use Pinterest. You can pin things that are similar to what you want your day to be like, and I and the other vendors can more easily match your vision.
Have a great consultation!