You may want to keep your tracking number handy - just in case.
As far as your return trip home, when making your purchases at gift shops (resorts or theme parks), you can choose to have your purchases shipped to your home address via UPS or FedEx. If this is something you're interested in doing, just inquire when making your purchase, and a cast member will be happy to assist.
If you are staying at a resort with a business center (Boardwalk Inn, Contemporary, Coronado Springs, Grand Floridian, Yacht Club and Swan/Dolphin) you can mail packages there. If you are not staying at one of these resorts, stop by the concierge desk in the lobby of your resort for assistance. Either way, cast members will be happy to assist you in getting your packages mailed home. There is a surcharge to cover the cost of shipping materials as well as the actual shipping cost.
I used the Coronado Springs business center option last December to mail two boxes home and found it extremely convenient.
Have a magical vacation! Diane :)