What should I pack in my pack?

Sunscreen and sunglasses (if it's a sunny day), a snack if you don't want to spend a lot on food, your phone, wallet/purse, and a water bottle. Don't buy water at the parks, it's expensive! Take one with you and fill it up at the drinking fountains. Optional things would be a waterproof cover if you plan on going on water rides, or on a rainy day, a plastic sandwich bag to put your phone and valuables in if you go on water rides, and a camera if your phone doesn't have a decent one. If you plan on taking a disposable camera, don't buy one at the theme park, as they'll be very expensive.