Welcome Back, Molly!!
It's so good to see you again, and thank you so much for sending another fantastic Disneyland Resort vacation planning question to us hEAR at planDisney!
As a Texan who is addicted to a certain Texas-created and Texas-beloved brand that isn't widely available outside of the state, I completely understand wanting to prepare in advance. I have some answers for you, Molly, but I also have a lot of tips. Disney Parks are Coca-Cola® beverage zones, meaning you'll only find their line of drinks. The most commonly found options are Coca-Cola®, Diet Coke®, Sprite®, Minute Maid Zero Sugar Lemonade®, and Fanta Orange®. These can be found at all table service dining locations as well as all quick-service locations.
Other sips found scattered at select locations are Gold Peak Ice Tea® (both sweet and unsweet), Barqs Root Beer®, Coca-Cola Cherry®, and different flavors of Powerade®. There are possibly a few others, but those are the most common. The best way to find out who serves these more specialty selections is to play around with the Mobile Food & Beverage Ordering feature in the Disneyland Mobile App. This is actually how I resEARched the options I just listed, and I'm in Dallas right now. When you open the app, press the plus (+) symbol at the very bottom of the screen. In the new pop-up window, select 'Order Food.' From here you'll see the list of dining locations that offer Mobile Ordering; what I did was select a location, select either a pick-up time or press 'Order Food', and then you'll be shown the full menu. (If you just click on 'menu' without selecting a pick-up time, you'll still only see 'assorted beverages', not that location's full list.) Scroll down to where the beverage options are and select "Fountain Beverages" and then you'll be shown all of the options available at that one location. (Don't worry, you won't be charged for anything as long as you don't add anything to your cart and back out of the ordering menu before you get to the final payment option.)
Pro Tips:
~ For locations that don't feature Mobile Ordering quite yet, they'll have a signboard outside of their entrance notating their beverage options.
~ Some Quick-Service dining locations, usually the ones where you grab a tray and go through the line 'cafeteria style', offer beverage stations where you can fill your cup yourself. This not only means free refills (for that mealtime) but it also usually means that they'll have more beverage selections. These locations are Alien Pizza Planet, Plaza Inn, Rancho Del Zocalo Restaurante, and Boardwalk Pizza and Pasta.
~ I can think of two locations resort-wide that offer Coke Freestyle® Machines, which offer dozens of combinations. One is at the GCH Craftsman Grill and the other is in a little nook of the shop located directly across from Soarin'.
~ Lastly, outside food and drinks are allowed in the parks. The rules around bringing your own beverages are no glass containers, and if you bring something to keep them in, like a cooler, it can be no bigger than 24" long by 15" wide by 18" high. Loose ice is also not permitted, but you can bring ice packs or ice in large baggies.
I hope this helped to quench your thirst, Molly, and if you have any more questions about your upcoming Disney Days, We're All Ears!
~Kristen N.