Many horse's moods vary from fair or antsy to bored. Or, they just don't behave. Having spent a few years taking a few different horses to fair, I have tried many different things to keep a calm happy horse.
1. Walk them around.
2. A toy.
By walking them around, you are installing a sense of control in them. Eventually, they no longer see it as a bad thing and more of an adventure. Let them see all the sights allowed and allow them to smell everything. This gives them a sense that "hey, this ain't too bad and I can handle this". A little at a time. If your horse is anxious at first just walk the length of the barn a few times till the horse has settled down.
Get them a toy to play with. I don't mean run out to Tractor Supply Co and buy one. I mean just something. A suggestion I used this past year was treats in a clean milk jug. It worked. The smell and promise of a treat kept horses happy for hours. A ball. Another great trick I use is a pink horse ball, but I have seen footballs, soccer balls, and basketballs in the stalls with other horses.
Spend time at the stall with your horse. Groom them, pet them, talk to them. Just be there. You are the most constant thing for them before and after fair so be there during fair. Now I'm not saying don't go enjoy the fair. No, do. Just manage your time wisely so that your horse gets your time too.
And exercise them. Go to the arena, the track, or where you can and make the horse work. Lunge them, ride them, push them to realize this isn't any different than home. Exercising can be the best thing for you and your horse to build the confidence in the fair experience.
*Image courtesy Flickr creative commons.