Bravo for taking your boy with you, your going to have a blast. Do, take cash, cash rules. Don't, leave without buying something.
I'm guessing you'll have this next one covered but thought I mention it anyway. Do, take a shower and brush your teeth before leaving the house for a show. I can't tell you how many shows I've been to where some smelly/stinky people think it's ok to attend that haven't bathed for a week and/or are wearing last weeks clothes. I'll leave the crop dusting topic for another thread.