You can eat as much as you want! I had two lunches lol! There are basically food and drinks everywhere all day - you just walk up to the restaurant or a refreshment cabana and ask for whatever you want (The refreshment cabanas have baskets of chips, fruit, cookies etc that you can just help yourself to as well as other snacks you can ask for like ice cream, hot pretzels etc). My personal favorite were the frozen cocktails! If you're over 21 that will be noted on the little ID card/lanyard they give you in the morning that you have to wear at all times so you don't need to worry about carrying your ID with you.
As far as the food and drink goes, DC really has it covered - you will not go hungry or thirsty and you will always be near refreshments.