Hello Daisy!
How exciting to be planning your first Walt Disney World vacation. Congratulations! You are going to love visiting in the fall. The decorations are beautiful, the weather is a bit cooler and the crowds are historically lighter. Autumn just happens to be my favorite season to visit Mickey and his pals!
Unfortunately, distilled water is not available at the resort, but you can use a grocery service like gardengrocer.com or order from amazon.com and have them send it directly to your resort. Resort addresses can be found on the Walt Disney World website, or by calling (407) 939-5277. (It is helpful if you are able to mark the package as "Guest" and add your check-in date.)
Mickey's Not-So-Scary Halloween Party is one of my family's favorite events and yes, they will provide bags to collect your candy in. You will have quite the spook-tacular time trick-or-treating through the Magic Kingdom and make sure you see Mickey's "Boo-To-You" Halloween Parade it is ghoulishly great!
Have a boo-tiful vacation, Daisy, and if there is anything else I may assist you with,
please ask me another question.
Happy Planning,
Lauren