Should I bring lots of gaming books? Do I really need to sleep while I'm there? Trail mix is OK food, right?
I will give you advice in terms of my 2009 visit to Gencon.
Is this a large convention? You will want a good pair of shoes with a fair amount of tread on them. You may want to consider getting some new insoles if a lot of walking will be involved for more than a day.
Invest in a backpack that allows you to insert a water reservoir or get a good water bottle that is not too troublesome to carry. Regardless, get a sturdy, comfortable backpack to hold your gaming materials and purchases.
Larger conventions can be loud and busy. Be sure to give yourself a break a few times a day for at least 15 minutes. Get a snack, sit on a bench, or just take a breather.
Organize in advance with your travel companions! Do not wait until you are at the convention to decide what events you want to do. Work out any shared hotel arrangements at LEAST two weeks before the convention. Know when everyone intends to arrive and leave so nobody gets stranded. If you are capable of securing your own room, do so. You will not regret it and enjoy the comfort, peace, and quiet.
Did you pick out some events? Get there ten minutes early. If it's a high demand event, get there half an hour early (True Dungeon, panel w/ Monte Cook, etc).
Carry a light snack or two in your pack. Consider the dining options in town. Things closer to the convention area will be more expensive with long wait times.
Try something new! Pick out an event or two from a game you've never heard of that sounds interesting. Many games are being presented by members of the company behind the game and in some cases the game designer themselves.
Be prepared to spend $100 more than you planned on in the dealers area. There are shiny things you did not know even existed in here and you will want them.
Bring a camera. You'll see people in costume, amazing artwork, and/or oddities you will want to remember.
I'd add "bring some cash." Many vendors aren't set up for credit/debit cards and are reluctant to accept checks from someone who may live 1,000 miles away. There will be things you want to buy. I don't buy much in the way of gaming product, and there are always things I want to buy.
Create a packing checklist well in advance of the con. Add to it as needed. Otherwise, you WILL forget stuff.
Before you go, do some websearching to figure out where you can eat near the con. Don't leave this till you get there. You might not have internet or whatever. Print a local street map. You might also want to know where the local FedEx or other copy center is.
If you have lots of friends and a smartphone that can do Twitter, set up a twitter hashtag for coordination with your friends: "i'm running dnd at embassy suites at 9 #genconfools"
Four hours of sleep is for young kids, and you're no spring chicken. Get seven. Don't overschedule yourself and you'll enjoy the events you attend far more than you will if you're exhausted.
At GenCon or some other big con, leave at least one whole event slot wide open. You'll want to spend some time browsing the goodies in the exhibit hall. Check out everything the con has to offer: the art show, the wargaming, boardgaming, computer games, card games, and so on. Even if you don't participate, just seeing this stuff is cool (wargame dioramas RULE).