I highly suggest bringing in a pillow, treats, healthy snacks, fruits and also a lunch if you have a full day sitting.
A good nights sleep and Meditation is the best way to deal with the pain of a tattoo, I would suggest practicing meditation at home so that you can use it to your advantage during your tattoo process.
It is important to learn to stay calm during a painful experience, if you are calm, the pain does not bother you nearly as much or at all. Yoga can also help by strengthening the body and mind.
Numbing cream is not recommended, it is at the clients liability if they are to use numbing cream, using numbing cream might void a free touch up, it is unknown to me if it affects the consistency of the skin.
Numbing cream may only work for a couple of hours and sometimes not at all.