Welcome to planDisney, Jenna! I'm so excited to hear that you have a trip planned to Walt Disney World Resort this coming December. The week between Christmas and the New Year is a very exciting time to be at The Most Magical Place On Earth, so make sure to use some of your time to enjoy all of the 
holiday festivities that will be going on!
If you're not staying at a 
Walt Disney World Resort Hotel and you'd rather not purchase 
MagicBands, that's perfectly fine. You can use your smartphone and the 
My Disney Experience app to manage your 
admission, order food using 
mobile ordering, access your 
Disney PhotoPass photos. A MagicBand is not a necessity in the Theme Parks but they are available for purchase at most merchandise locations if you decide that you want one. They can be reused on your subsequent trips, so if you come back and decide to stay on-property, you'll be able to use it to open your Resort Hotel room door and make charges to your stored credit card. Aside from a few attraction photos, like 
Haunted Mansion and 
Seven Dwarfs Mine Train, there aren't any experiences that require a MagicBand so feel free to make the best decision for yourself and your family next month!
I hope this answers your question, Jenna, and please let us know if there's anything else we can do to help you plan your magical vacation.
Jessica