Aloha, Candice!
Thanks for stopping by the Disney Parks Moms Panel. How delightful you are going on a moms outing to the Happiest Place on Earth! Disneyland Resort is very accommodating to families, babies, and nursing mothers. You will be able to peacefully and privately pump milk for your little one in the
Baby Care Centers located in Disneyland Park and Disney California Adventure Park. For milk storage, you can ask if it can be stored in the Baby Care Centers, but I advise packing a small cooler with ice packs and storing it in one of the convenient
locker rentals located in either park or outside the parks in the esplanade. This would also be a good location to store your pump supplies throughout the day as well. You can use these lockers as often as you'd like throughout the day for the same low price. Keep in mind that only small coolers are allowed in the parks and must be no larger than 24" long x 15" wide x 18" high. If temperatures are hot, you can always request complimentary ice cups from any of the Quick Service locations on property as well.
Since in and out privileges are a benefit of every
Disneyland Resort park ticket, you may also leave to drop off your milk at your hotel refrigerator if nearby and return back later in the day. I often leave the parks at least once a day to change my clothes or drop off souvenirs I have purchased.
Since you will be on an adult's only trip, I suggest visiting some of the wonderful lounges like Napa Rose Lounge or Trader Sam's Enchanted Tiki Bar! I hope some of these ideas help you, and I can't wait for you and your friends to enjoy a magical day.
-Jennifer