Disneyland is a little stricter than Disney World when it comes to bringing your own food into the park. In Anaheim, there's a designated picnic area outside the main entrance to Disneyland Park where people are encouraged to bring their own food and eat before entering the parks. As long as you don't enter the park on an empty stomach, you're guaranteed to save money on snacks.
However, at Disney World, you're allowed to bring food into the parks, including perishable foods in a cooler. Pro tip: you can rent a locker inside the front gates of all the parks and keep your food there until you're ready to eat.
It can be hard to find meals that accommodate dietary restrictions at Disney parks, including kosher foods and gluten-free meals, so keep that in mind as you're planning your visit. At Disneyland, kosher meals must be requested 24 hours in advance of dining at a restaurant.
