We bring lots of snacks in our luggage from home for my nieces and nephews. They are usually things that they don't get at home like Ring Pops, little packages of Oreos, snack pack Peanut M & Ms, bags of chips, as well as some healthier options like granola bars, peanuts, raisins. Each kid on the trip is allowed to pick 1-2 snacks for me to purchase, but once we get there they are up for grabs for anyone including the adults.
When we get to the hotel, we designate one drawer as the snack drawer. The kids can take as many snacks as they want into the park, but they need to carry their own snacks either in their pockets or a cinch bag. They can eat the snacks when ever they choose, but once they are gone they are gone. My oldest niece used to eat all her snacks in the first hour at the park because she slept too long to get breakfast! I would say typically everyone takes about 3-5 snacks.
The kids look forward to having the extra "treats" that they don't normally get at home and this method gives them some control over what and when they eat. Eating snacks in a ride line or while waiting for a parade alleviates some boredom and stops the "I'm hungry" complaints. I also don't like wasting time in long food lines if I don't need to.