Hello, Chris! Thanks for bringing your question to the Disney Parks Moms Panel!
I am so glad that you and your son will be enjoying all the magic and wonder of the Happiest Place on Earth this summer! You can certainly bring in your own food to accommodate your son's dietary needs. The only restrictions that the Disneyland Resort has is that you can't bring any food items that are packaged in glass containers (small baby food jars are the only exception) and you can't bring in alcoholic beverages. If you will need to bring a cooler for your son's food, please ensure that it is smaller than 24" long x 15" wide x 18" high to be in compliance with
Park Rules. You are welcome to carry your cooler around with you, but storing it one of the many
lockers available to rent might be more convenient.
As far as the cart-like wagon you describe, the official stance is that wagons of any sort are prohibited. However, since your son has special needs, I encourage you to call Disability Services at (407) 560-2547 to discuss your situation. They might be more familiar with your particular device or be able to provide other solutions that will fit your needs. I would also check out the
Services for Guests with Disabilities page to read up an all the resources available to make your trip go as smoothly as possible.
I hope this helps! Have a magical time at the Disneyland Resort!
-Linda