We walk in with everything we need in our pockets. Tie a hat to your belt loop and if you want carry one bottle of water in to the park to start the day with. There is a no bags lane to enter the park that is much faster and when standing in line for 2 to 3 hours for a ride things get heavy. Part of the fun of Disney is to get to spend money on junk food you don't normally eat. When staying in a Disney hotel the shops will send purchases of souvenirs to your hotel. If you have to bring something in and don't want to lug it at the front gates there are lockers for rent but it is a real hassle if you are across the park when you need it. The night before you hit a park go over what everyone has to see or ride and do those first. The earlier you get in to the parks the better they get more crowded as the day goes on.
You are not allowed to carry small food items (like granola bars or small snack bags) and bottles of water. They will not allow you in with a cooler full of drinks and food. All bags get searched prior to entering the turnstiles.
First thing you want to do is run like hell for a fast pass to Tower of Terror, Rock N Roll coaster and or Test Track. Get the pass and hit whatever popular ride first and fast pass the second ride. After that you are screwed as the passes will be gone and the two hour per ride wait begins.