Hi Kassandry,
When you purchase a Magic Your Way vacation package, your park tickets will be included on your Key To The World cards which also act as your hotel room key. Your Key To The World cards will be given to you when you check-in at your Disney Resort hotel.
If you arrive at your Disney Resort hotel before your hotel room is ready, you can absolutely check-in, collect your Key To The World cards, leave your luggage with Bell Services and hit the parks straight away.
When you return to your Resort hotel later that day/evening, you can simply collect your luggage from Bell Services and make your way to your hotel room.
If you would like to be at the parks as early as possible on your day of arrival, I would recommend that you complete on-line check-in before leaving home. Online check-in can be completed from 10 days prior to your arrival date and you will find that by doing this, it will speed up the whole check-in process when you arrive at your Disney Resort hotel.
Wishing you a magical trip filled with memories which will last a lifetime!