Hi Anne and welcome to the Disney Parks Moms Panel. We are clearly meant to be friends, because I am literally writing this answer while surrounded by snacks I purchased for my upcoming Walt Disney World Vacation!
Anne, in my opinion, water is an absolute must when visiting Walt Disney World. My family always brings our refillable water bottles with us, and you won’t have any trouble getting through security with them, as most everyone brings water. Free iced water is available at most Quick-Service locations, and you can also refill your bottles at water fountains around the parks. (My kids call Florida water “Pirates of the Caribbean water” because it tastes just like that attraction smells – magical water!)
You’re also welcome to bring snacks into the theme parks. Be sure to take a look at the
Park Rules so you’re not bringing prohibited items like glass bottles, and also remember that unless you rent a locker, you will need to carry the snacks with you in a cooler or backpack (also look at the Park Rules for sizing regulations for those).
While I don’t know of any theme park refillable mugs, there
are refillable popcorn buckets. Popcorn refills are widely available and very inexpensive – and somehow even the popcorn in Walt Disney World tastes pixie-dusted. You’re right that the Resort Refillable Mugs, which come with the Disney Dining Plan and can also be purchased separately, can only be refilled at the resorts, not in any of the parks.
Anne, make sure you leave room for the delicious treats that can be found around the parks – from specialty cupcakes to Mickey-shaped pretzels and ice cream to the iconic Dole Whip, you’re sure to find the perfect snack!
Wishing you a magical vacation,
Robyn