Well, commodorified covered just about everything anyway. :) I would reiterate that eating before you go is a great idea, and having something to snack on after can be helpful; but I mean, I did about seven hours in the chair at my peak inking, and that's when you really need to be aware of how tense you are for long periods of time! If your tattoo is small and the artist estimates it'll be under half an hour, you should be perfectly capable of handling your body's reaction. Get iulia to hang on to water for you, and you should be sorted.

Good luck. Tattoos are the best thing in the world, and I hope you love yours.