As, everyone else said, everything but food, mugs, towels and lockers! Since it seems to be your first time going to a water park, I have some real quicky tips for you.
1. Get there early. You may think "yea, yea to be the first ones to ride," but that's not exactly why I am saying this. You'll probably want a place to put towels, sunscreen etc, for easier access. They do offer chairs, but they fill up, FAST, you'll want a good one, trust me!
2. Watch out for the waterfalls if you HATE cold water. No, it's not even water, it's liquid ice
However, they are great ways to annoy your sister with by pushing them under one! If you find yourself in a bad situation, find the nearest kiddie tube and place it over your head! The have no hole at the bottom! KIDDIE SHIELD OF LIQUID ICE!
3. Water shoes, if you have them, bring them. The pavement gets HOT! Yes you can take the amazing lazy river as a nice, refreshing transportation system, but there will still be steps and concrete! And, no, no matter how hard you try to dampen your feet, you WILL feel the pain!
4. WARNING, Go to the bathroom with shoes! There is nothing more disgusting than walking on a slimy, wet bathroom floor. Yuck!
5. If you go to BB, (which you can go to both TL and BB with a pass) watch out for the Summit Plumit. Unless you have a butt of steel, I would save it for last! I will hurt , because they don't just 'gush' water down, they go all firehyrdron exploding on you water gushing down! Still a amazing slide though, painful but worth it.
6. Lazy river= Monorail of the the water park.
7. Food- Eat during the slightly more crowded part of the day. It'll be less crowded when you eat because everyone else is on the rides!
8. Have fun!
Sorry, that wasn't so quick but, a few of those tips will make some gigantic impacts on your day at the parks!