Ahoy, Trina!
Welcome to the Disney Parks Moms Panel! You are going to have a WONDERful time sailing to Alaska with Captain Mickey and his friends! My son has food allergies as well as special needs and we've found that Disney Cruise Line does an incredible job at trying their best to accommodate his needs.
I do know that Disney Cruise Line has soy milk available onboard; however, I'm unsure if they carry vanilla flavored soy milk. I highly recommend giving the Disney Cruise Line Special Services Team a call at (407) 566-3602 and speak with an agent about your son's particular
dietary needs as well as food allergies. The Special Services Team will be able to tell you if vanilla soy milk and soy yogurts are available on your voyage. With 60 days advanced notice, they could possibly order a limited number of specialized food items from their vendors and have them onboard for your son at no additional cost to you!
Trina, you may also bring vanilla soy milk and soy yogurts onboard with you! You just need to make sure they are sealed in their original packaging and carried on with you in your carry-on luggage upon arriving at the Cruise Terminal.
Coolers are also allowed for dietary restrictions, baby food or medications only. If you'd like to pack the vanilla soy milk in a cooler as your carry-on luggage, you may do so! Just be sure your cooler does not exceed the measurements of 12"x12"x12".
I hope I was able to help you plan for your vacation of a lifetime! I can't stress how invaluable the Special Services Team is! Please give them a call before setting sail!
Beth