I play almost exclusively live tournaments. I always take a back pack with snacks, Advil, pen, paper, sometimes a drink but a lot of casinos
won't let you bring drinks in, $1 bills to tip the waitress, my phone, iPad
, earphones, a sweat shirt (always dress comfortably and in layers because you never know how hot/cold you'll be), sunglasses in case I want them, chapstick, basically all the things I need to make myself comfortable for 12 hours. Make sure you bring enough cash.
I always use a card cover, especially if I'm in the 1 or 10 seat as thats the more likely spot for a dealer to accidentally muck your hand.
Always announce your raise before you put chips out. I can't tell you how many times even seasoned live players get in trouble for this and the rules about if you can put more chips over the line than you want to bet. Best to announce first.
Just be nice to everyone and if you don't know something don't be afraid to ask. It wouldn't hurt to familiarize yourself with TDA rules.
Those are some of my tips, good luck!