Last year we took a huge cooler on wheels packed full of snacks, sodas, and subs. We never had any trouble, but when we entered they asked if they could check it.
We brought a cooler with food, snacks and drinks. They took a quick look and we were on our way. NO GLASS!!! CM's didnl't even give it a second tought. We were at Blizzard Beach.
Jim
Both water parks allow picnics as long as you don't bring in any alcohol or glass- and they will check your cooler. We have always done this since the food at the water parks is awful.