Hi, Hiranya! If you are staying at a Walt Disney World resort, they will hold your luggage for you until it is time to depart. You won't have to worry about carrying your bags into the theme parks or to Downtown Disney for some last minute souvenir shopping!
If you are using Disney's Magical Express, they will pick you up at the designated location at the front of your resort approximately three hours before your flight. There are some airlines that will even allow resort check-in, so you can take your bags to the check in location, get your boarding pass, and when you arrive at the airport, go directly to security.
You can find more information on Disney's Magical Express and the list of airlines participating with Resort check-in
HERE.
One last thing - you can sometimes get a late check out at the Walt Disney World resorts! On the morning you are due to check out, you can call the front desk. If it's at all possible, they will extend your check out time to 1:00 PM. This will allow you a bit more leisure time in your room.
Have a great vacation!