1. I wouldn't recommend leaving your snake in the car unless someone is there with the snake and can alter the temp in the car to keep it optimum.
2. sometimes, disease can't be prevented by simple handwashing. Like for mites, they can jump onto your clothes and then onto your snake. Handwashing won't stop that.
Ultimately it's up to you whether or not you bring the snake (assuming the expo will even allow outside animals) to the expo. Honestly, I would take your snake to a vet to have it sexed, find someone close to you to show you, or have someone at the expo show you so you can turn around and sex your snake. If it were me, I wouldn't bring my snake anywhere near an expo, but that's just me.