Hey there Miriam,
Welcome to planDisney and thanks so much for your question! It sounds like you're already hard at work planning your next visit to the Happiest Place on Earth during the Halloween season. Three days in September will be so much fun and the weather should be fantastic!
When you're purchasing your
theme park tickets, you will have the option to add on the
Park Hopper and
Lightning Lane Multi Pass options during the purchase process. Plus, it will also walk you through setting your
park reservations for each day of your visit.
If you choose not to add these two options on when you make the ticket purchase, then you can add the Park Hopper option between your purchase date and your actual visit. You'll want to
call a Cast Member at the Tickets line to get this taken care.
For the Lightning Lane Multi Pass, you would need to wait until you scan your ticket to enter a park for the first time during visit if you don't purchase it together with your tickets.
If these options fit your budget, I highly recommend both of them as they add quite a bit of flexibility and convenience to your visit. Plus, they pair together nicely since you're able to park hop to access Lightning Lane queues in both parks. Not to mention the extra perk with the Lightning Lane Multi Pass that provides you unlimited digital downloads of all your
PhotoPass photos during your trip!
Thanks again for your question, Miriam! I hope you have fun planning your trip and even more fun during your visit!
Have a Magical Day,
Greg