Mike Cavanaugh already gave some stellar advice, but I'll just reiterate a couple that I think are especially important.

Definitely have a care sheet you can pass out! Many will be looking to buy their first snake, so give them information, as well as putting sites like this one as a resource is a good idea.

Also giving out a business card or something similar with your contact info is good. I've gotten several repeat customers that way, as well as they'll give your info to people they know looking to buy, so you can get customers that way, too. It'll really do a lot for you.

And hand sanitizer is a must IMO!!!!! People will be handling lots of animals and you want to minimize risk of contamination.

Also bring lots of change (ones, fives especially). At shows I've ended up not buying something from vendors because they couldn't provide me change. Most recently at a show I was going to buy a corn snake and we had agreed on a price of $65 - I gave him $80. He didn't have the $15 in change, I didn't have anything but $20's, and he didn't want to go to $60. So I walked away. At that point wasn't worth the effort of me running around trying to break a $20.