From their website:
IS ALLOWED:
Small ice chests of six-pack size or smaller (one per family)
Special dietary food, diabetic, health related or dietary needs. These types of specialty foods may enter the park with park management approval
Baby food, bottles, jars and other baby items
Fountain drinks, single serve drinks, refillable mugs (if opened prior to turnstile)
Reasonable quantity of bottled drinking water. Juice boxes (straws must be disposed of)
Single servings of snacks
IS NOT ALLOWED:
Alcohol is never permitted in through or out of the turnstiles. Any alcohol from outside of SeaWorld must be disposed of prior to entry. Any alcoholic beverage purchased at SeaWorld must be disposed of prior to exiting through the gates.
Ice chests larger than six-pack size
Straws and lids
Bags of fast food items, picnic baskets, sandwiches or loaves of bread (meals)
Soda, sports drinks or energy drinks (single serving is allowed if open)
Large servings of snacks