Congrats on your first con being Akon, it was mine too.. but...that was a very very long time ago (Akon 7..holy crap I'm old!)
Considering that it's akon, which is gigaaaantic.. my information for you is based pretty specifically on that convention, but would apply to most.
The area of town the convention is in does not have a whole lot in the way of places to eat in the evening, so bring snacks and things that are easy to make in your hotel room, a cooler with some sodas, water, and snacks is your friend. Make sure you remember to eat and drink plenty of water. There are some places, but they tend to close early or not be open on the weekend as the area is primarily used by weekday businesses. There is a restaurant in the hotel, but it is more then you will likely want to pay.
The con is exciting and it's easy to forget to sleep and drink water, then suddenly you will wonder why you are cranky and have a headache and don't want to go to that 2am video room, so try to bring a water bottle with you when possible and not fill up on too much ramune.
Don't forget your ID card and -cash-. There are panels and video rooms (hentai/yaoi etc) which require you to show proof of age, not to mention that you may need it to show for your badge, paying at vender tables, etc.
Even if you preordered, make sure you show up -early- friday morning to get your badge (like seriously.. 7/8 am) otherwise expect to be in line for several hours.
When you do get your badge, keep it on you at all times, you never know when you might want to pop into the dealer room or some other place which requires badges to access. Though be careful not to misplace it!
Don't take anything you aren't prepared to loose, forget, have stolen. Though it is rare for people to pickpocket, it is very crowded and you just never know what might happen, so don't finish off that costume with your great grandmother's wedding diamonds.
General safety rules apply, don't get too excited about being around all these awesome people that share your favorite shows and forget that they are really all complete strangers. Don't go places by yourself and make sure you have a meetup plan with your friends. Cellphone reception within that particular building is very difficult, not to mention the noise makes it hard to even realize you've had a call.
Wear comfortable shoes, this goes double for if you are staying on a high floor of the hotel. Though in the last few years they have been very good to keep an eye on elevator usage, there is a long history of the elevators breaking at some point and anyone staying in the hotel having to use the stairs to reach their room. There are also times when the direct access between the convention and the hotel is shut off, and you have to walk outside to access one from the other (this is typically late at night).
Though because of the elevator monitoring, please take into account that getting up to your room may take longer then at a normal hotel, as you might have to wait in a long line.
-cosplaying specific tips-
Since you say you are planning on going in costume, bring a little sewing kit, safety pins, duct tape, or whatever else you might need to emergency patch something. Remember that a costume still has to fit in with the other dress code rules at the convention (shoes, shirt, etc).
And when you pose for pictures, do it in an area that does not block the flow of traffic near the escalators or doors, people will do their best to stay out of the way of your cameras, so return the favor and do it out of main walkways.
Though 'glomping' is down in general, you may have someone randomly hug you. This type of behavior is really looked down on, and you have a right to tell people you don't like it and not to do it and to defend yourself with an arm or such if you see them coming. In general people will just snap a picture of you, tell you how cute you are, then move on.
Primarily... bring cash (some comic dealers will give you a discount not to mention it's less hassle), remember to eat, remember to drink plenty of water and take breaks for naps and potty, don't go full tilt 72 hours solid, and wear comfortable shoes.
Have a good time at the con, there are lots of really awesome people there, and if you can live through an Akon, then you can live through -any- con.