I have done this a few times- and I have learned a few lessons which I will pass on here.
ALWAYS use a carrier like FedEx, UPS, etc. NEVER use the US Postal Service. Here's why.
The carriers deliver directly to the resort itself- it's the quickest, most direct way to ship.
No matter where your package is addressed to- if it's on Disney World property it will go to a mail clearinghouse and be sorted from there. That adds several days (at least) to delivery time. And you really can't track the package either. As I found out, if you use "delivery confirmation" it tells you when it has reached the clearinghouse. That counts as being delivered. Then you have no idea where it is anymore.
But FedEx or UPS are terrific.
Address the box to the resort. Call the front desk (use Info Central's resort phone list
to find the phone number) for the exact address. You will also be asked to put your last name, reservation number and arrival date on the lower left corner of the package. Bell Services will hold your box until you arrive.
I would time it to arrive 1-3 days before you do.
Also- remember to pack an address label to send it back home and some packing tape as well. You can bring the box back to the front desk and they can arrange for it to be shipped out again.