If most of the people use a canopy you should invest in one, too. It provides rain and sun protection and looks professional. I also put some old carpeting on the grass in my display and made it look elegant. I tossed the carpet at the end of the show. (These suggestions are for outdoor shows.)
Keep your change box out of public view. Never let anybody see what's in it. I had a small crate, covered with a cloth and facing the back of the display and on the table all the way in the back of the display. My change box sat in it when I was making change. I could open it and since it was inside the covered crate (that was resting on the side with the opening toward the back of the display) nobody could see the money inside or watch me counting change. Always lay the money you are handed on the top of the box or someplace separate from your own money. This way if the customer says or thinks they gave you a $20 instead of a $10, you can pick it up and show them that this is what they gave you. You can even leave their money visible to them so that there is no question that that is what they handed you. You should determine your check accepting policy. I asked for phone number, but sometimes they didn't want to give it. I talked to another vendor who said in that case they would refuse the sale. But in the 20 years I crafted, I never had a customer's check bounce.
Some crafters wear an apron with a roomy pocket and keep their money in this. Especially a zip or velcro pocket would be nice. Keep your change box out of sight and covered and inaccessible when not in use.
I read a sad story of a crafter who was packing up to leave and had his money box stolen from his truck, so do not let it out of your sight- there are people who may actually know how craft sales work and who will watch for the money box to be left alone for a second.
If you don't have a helper, maybe the people on either side would be willing to watch your things while you take a bathroom break. They don't even have to sell, just keep and eye and tell customers that you'll be back shortly. If you don't have a helper, you should stay at your booth except for bathroom, in other words, bring your own food and water. When you are away from your booth you may be losing business, and you can't expect or want a stranger handling your money box.
Don't put your most expensive items in front. People see the high price and it may turn them off. Do price everything. I often will walk away rather than ask the price. And you are busy helping a customer, a potential customer may really not want to wait around and ask.
Refuse to hold an item when customer asks if you will "just a little while". A couple times I put an item aside and the customer never returned. I was being nice, but I lost sales. So you could say, OK I'll set it aside but only until (a half hour from then.)
Do you have or need a sales tax number? If so, do you have your tax table?
At one time I gave sales slips. The last few years I didn't and just jotted down the sale on a sheet of paper.
If it is an outside show bring bug spray. Bring some toilet tissue, in case, If there are portapots bring hand wipes.
Make sure your breath is fresh. Don't leave food or drink items sitting on the display. Have an area of the display that is clear so people can write checks on it.
Don't chat with a friend while there are customers nearby, it looks unprofessional and may cause people to leave. Bring plenty of bags.
Good luck with your show!
I took him over to the gourmet dog cookie booth twice to "pay him" for his hard work 
He had people coming into the booth right and left asking if they could hug the cute doggie and then he would sit there nice as could be while people tried collars on him.
