Those are your key to the world around your wrist! They contain your park tickets, room key, dining plan and reservations, Lighting Lane selection passes, and credit card charging capabilities if you select that option.
Magic Bands are not required for your Disney World vacation. You have access to all that a Magic Band can do within the MyDisneyExperience app on your smart device or you can request a Key to the World card be printed at the resort front desk after check-in. If you're not staying on property, you can pick up your ticket cards at any theme park entrance guest services window.
Many people do like having a Magic Band during their trip for ease of having everything right on your wrist, but it's a personal preference. If you have a Magic Band 2.0 from a previous trip, you can reuse it for an upcoming trip.
Learn more about Magic Band+ (3.0) including setup details and all the magic that's within each band!
Magic Bands can also be purchased while on-property and linked to your MyDisneyExperience account for immediate use.