A nalgene bottle of water in the staging area should be fine for about half a day 3/4 of a day if you stretch it out. Preferably get a few bottles of water and toss them into a cooler if you can, cool water is really refreshing especially when it's a hot day.
Get a camelbak if you can. CP gear sells the pack in CADPAT, OD, and tan IIRC. All you need after that is a bladder (2-3 Litre is really good). Don't have to have the camelbak on you on the field though, in the staging area should be good enough.
If you're not sure about hits call it. You don't want to be known as the "cheating underager" even if it wasn't intended.
Listen to the field marshals and admins, and show respect, you will get it back in return. Ask questions if not sure, but don't bug people with every stupid ass question you can think of (like alcohol a little bit is good, too much is bad).
Prepare to get dirty. Bring a change of clothes, you don't want to have to wash/vacuum the car after a long days game.
Bring a lunch if not provided, not like an Oh-Henry bar and coke but something more like, go to Safeway and pick up some lunch meat, tomatoes, lettuce, etc. and make a sandwich with that, doesn't have to be anything special but good nutrition should keep you running for the whole day. Hey you can even pick up those "lumber jack" sandwiches at Safeway to save you the trouble of having to make a sandwich.
DO NOT under any circumstances be condescending or anything, act normal (well, act normal enough....) you're in the eyes of the other players so make a good impression, even a meh one is good enough, don't leave a bad taste in their mouth is pretty much what you should be aiming for.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE