Lee,
Since this is your first event, I'll offer the following suggestions as I have learned during my first season doing events.
1) Have a chair so you can sit when you have a chance, it makes for a long day to be standing the entire time.
2) Have bags for buyers to put their purchases in
3) Have a pen and paper to take orders, notes, etc.
4) Take a cooler with beverages and snacks. Again, it's a long day.
I assume it's an indoor event?
If it's outdoors, be sure to have a way to weigh down your tent so it doesn't blow away in a gust of wind.
Any other words of wisdom to share from the collective group?